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How to control the color difference of injection products?

Core Tip: Color difference is a common defect in injection molding. It is not uncommon for the injection molding machine to be scrapped in batches due to the color difference of the matching parts. There are many factors affecting chromatic aberration, involving raw material resin, color masterbatch (or toner)

 Chromatic aberration is a common defect in injection molding. It is not uncommon for the injection molding machine to be scrapped in batches due to the difference in color of the matching parts. There are many factors affecting chromatic aberration, involving raw material resin, color masterbatch (or toner), mixing of color masterbatch with raw materials, injection molding process, injection molding machine, mold, etc. Because of the wide range of exposure, color difference control technology is also recognized as difficult in injection molding. Master one of the techniques. In the actual production process, we generally control the color difference from the following six aspects.

    1. Eliminate the influence of injection molding machine and mold factors

    To select an injection molding machine with the same capacity as the injection molding product, it is best to replace the equipment if there is a problem with the dead angle of the injection molding machine. For the mold casting system, the exhaust groove, etc., the color difference can be solved by the maintenance mold of the corresponding part of the mold. The injection molding machine and mold problems must be solved before the production can be organized to reduce the complexity of the problem.

    2. Eliminate the influence of raw resin and color masterbatch

    Controlling raw materials is the key to completely solving chromatic aberrations. Therefore, especially in the production of light-colored articles, the significant influence of the difference in thermal stability of the raw material resin on the color fluctuation of the product cannot be ignored.

    Since most injection molding manufacturers do not produce plastic masterbatch or color masterbatch themselves, the focus can be on production management and raw material inspection. That is to strengthen the inspection of raw materials into the warehouse; the same product in production should be produced by the same manufacturer, the same brand masterbatch and color masterbatch;

    For color masterbatch, we must carry out sampling test color before mass production, both the same as the last proofreading, but also in this comparison, if the color difference is not big, can be considered qualified, as the batch color master has a slight color difference, can be The color masterbatch is remixed and then used to reduce the color difference caused by the uneven mixing of the color masterbatch itself. At the same time, we also need to focus on the thermal stability of the raw material resin and color masterbatch. For the poor thermal stability, we recommend that the manufacturer exchange.

    3. Eliminate the influence of uneven mixing of masterbatch and masterbatch

    Poor mixing of the plastic masterbatch with the color masterbatch will also make the color of the product change. After the masterbatch and the color masterbatch are mechanically mixed, when the hopper is fed into the hopper through the lower suction, the color masterbatch is separated from the masterbatch due to the action of static electricity, and is easily adsorbed on the hopper wall, which is bound to cause a change in the amount of the masterbatch during the injection molding cycle, thereby generating Color difference.

    In this case, the raw material can be sucked into the hopper and then manually stirred. For the addition of toner to produce colored products, the most effective way is to not use the suction machine, but use a hot air dryer to manually prevent the color difference caused by the separation of the toner from the masterbatch.

    4. Reduce the influence of barrel temperature on chromatic aberration

    In production, it is often encountered that a certain heating coil is damaged or the heating control part is out of control, and the temperature of the barrel is drastically changed to cause chromatic aberration. The color difference caused by such reasons is easy to determine. Generally, the heating ring damages and the chromatic aberration is accompanied by uneven plasticization, and the heating control part is out of control and often burns with product spot, severe discoloration or even coking. Therefore, the heating part should be inspected frequently during production, and it is found that the heating part is damaged or out of control and replaced in time to reduce the occurrence of such chromatic aberration.

    5, reduce the impact of the injection molding process adjustment

    When the non-color difference reason needs to adjust the injection molding process parameters, the injection temperature, back pressure, injection cycle and color masterbatch addition amount should not be changed as much as possible. The adjustment also needs to observe the influence of the process parameter change on the color. If the color difference is found, it should be adjusted in time.

    Avoid using high injection speed, high back pressure and other injection molding processes that cause strong shearing to prevent chromatic aberration caused by local overheating or thermal decomposition. Strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part close to the nozzle.

    6. Master the influence of barrel temperature and color masterbatch on product color change

    It is also necessary to know the trend of the color of the product as a function of temperature and color masterbatch before performing the color difference adjustment. Different color masterbatch varies with the temperature or color masterbatch of the product, and the color change law of the product is different. The color change process can be used to determine the law of change.

    Unless the color change of the color masterbatch is known, it is impossible to quickly adjust the color difference, especially when using the color tone produced by the new color masterbatch. 

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Special plastic PEEK injection molding

Core Tip: The molding temperature of this material is too high, and the damage to the screw is serious. When setting the screw speed, the speed should not be too fast. After the end of molding, the screw should be quickly cleaned with PE wax, and the material of PEEK should not be allowed to stay in the screw.

 The molding temperature of this material is too high, and the damage to the screw is serious. When the screw speed is set, the speed cannot be too fast. After the molding is completed, the screw should be quickly cleaned with PE wax, and the material of PEEK cannot be stopped at the screw.

    Molding temperature 320 degrees to 390 degrees

    Baking temperature 160~1855H~8H

    Mold temperature 140~180

    Injection pressure is 100~130MPa

    Injection speed 40~80

    PEEK features: high temperature fluidity and high decomposition temperature.

    PEEK is a semi-crystalline thermoplastic polymer with a melting point of 343 ¡ã C. PEEk thermal stability: it is difficult to detect PEEK decomposition volatiles when heated to 427 ¡ã C. Fourier infrared (FT-IR) detection of PEEK and CFR-PEEK composites The decomposition temperature is between 400 and 480 degrees Celsius, and there is no significant difference in thermal decomposition between the two. PEEK is kept at 400 ¡ã C for half an hour, the weight loss is less than 1%, and the temperature is kept at 360 ¡ã C for 1 hour without significant degradation. The long-term stable temperature is 340 ¡ã C (around the melting point), and the continuous working temperature is 160 ¡ã C.

    General-purpose thermoplastic processing methods are suitable for PEEK materials, including: injection molding, extrusion, molding, painting, and more.

    The general process of PEEK injection molding is as follows:

    1. Drying: The particulate polymer generally absorbs 0.5% w/w of atmospheric moisture. For best results, it should be dried until the moisture is less than 0.02% w/w. The material can be placed in an air circulating oven, dried at least at 150 ¡ã C for 3 hours, or dried at 160 ¡ã C for 2 hours. If it is dried in a dry box, the thickness of the raw material in the tray is not

    Can exceed 25mm. And prevent pollution.

    2. Recycling: The remaining material can be recycled and injected into pure materials. It is recommended that the recycled material without filler should not exceed 30% of the total weight, and the recycled mixture containing the filling should not exceed 10% of the total weight.

    3. Thermal stability: If the equipment is shut down during the melting process and the polymer residence time does not exceed 1 hour, there is no significant degradation of the material at a temperature of 360 ¡ãC. However, if the downtime exceeds 1 hour, the temperature of the cylinder should be reduced to 340 ¡ãC. At this temperature, the material can be kept stable for several hours. When the processing is continued, the temperature of the cylinder must be increased. If the downtime is more than 3 hours, The cartridge should be cleaned. Materials which are stable at 380 ¡ã C, such as polyether sulfone or polyetherimide, can also be cleaned with low MFI polyethylene.

    4. Injection machine: The melting point of the polymer is 343 ¡ã C, which can be applied to traditional machines that can keep the melt temperature at 360-400 ¡ã C.

    5. Cartridge capacity: Due to the high processing temperature of the PEEK polymer, the residence time of the material must be as short as possible. The ideal barrel capacity is 2-5 times the total shot weight.

    6. Nozzle and latching system: The melting point of the polymer is very high. If the temperature drops below 343 ¡ãC, the melt will solidify very quickly. Therefore, it is necessary to install a heater large enough at the nozzle to prevent the "cooling of the injection molding" from being caused by the cooling.

    7. Screw: It is recommended that the minimum length-to-diameter ratio L/D of the screw is 16:1, but the L/D ratio between 18:1 and 24:1 should be preferred. Professional plastic knowledge exchange WeChat group plus small series WeChat: NB58250988

    8. Barrel temperature: The unreinforced level is 360-380 ¡ã C, and the enhanced level is 380-400 ¡ã C.

    9. Mold temperature: The surface temperature of the mold is 175-205 ¡ãC.

    10. Injection pressure: The general injection pressure is 70-140 MPa.

    11. Injection speed: medium to high speed.

    12. Back pressure: It is recommended that the back pressure be set to 0-1.0 MPa (0-10 kgf/cm2).

    13. Screw speed: The general screw speed is 50-100 rpm. For the reinforcement level, it is recommended to use a lower screw speed.

    14. Mold shrinkage: Different grades of polymer have different shrinkage rates, the unfilled grade is about 1.2-2.4%, and the fill grade is: 0.1-1.1%.

    15. Secondary processing: secondary processing such as bonding, tapping, press-in, metal inserts, cutting and surface metallization.

    use

    It is a kind of engineering plastic with excellent comprehensive performance. The film can be cast or oriented, used as wire covered wire, atomic engineering component, H or C grade electrical insulating material, flexible printed circuit board, heat pump casing or frame, oil well. Couplings, valves, metal heat or anti-corrosion coatings, monofilaments, bandings, sieves, subways, mining, oil fields, electrical industry, atomic energy engineering, chemical equipment, etc.

    Peek is widely used in aerospace, automotive, electrical and electronics, medical and food processing.

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14 frequently asked questions in the field of mold manufacturing [1]

Core Tips: (1) What is the most important and most decisive factor in choosing mold steel? Forming method - can be selected from two basic material types. A) Hot-worked tool steel that withstands relatively high temperatures during die casting, forging and extrusion.

 (1) What is the most important and most decisive factor in choosing mold steel?

    Forming method - can be selected from two basic material types.

    A) Hot-worked tool steel that withstands relatively high temperatures during die casting, forging and extrusion.

    B) Cold working tool steel for blanking and shearing, cold forming, cold extrusion, cold forging and powder press forming.

    Plastic - Some plastics produce corrosive by-products such as PVC plastic. Condensation, corrosive gases, acids, cooling/heating, water or storage conditions caused by prolonged shutdowns can also cause corrosion. In these cases, it is recommended to use a stainless steel die steel.

    Mold Size - Large size molds often use pre-hardened steel. Integral hardened steel is often used in small size molds.

    Mold use times - long-term use (> 1000000 times) of the mold should use high hardness steel, its hardness is 48-65HRC. Medium long-term use (100,000 to 1,000,000 times) today's focus:

    The mold should be pre-hardened steel with a hardness of 30-45 HRC. For short-term use (<100000 times), the mold should be made of mild steel with a hardness of 160-250HB.

    Surface Roughness - Many plastic mold manufacturers are interested in good surface roughness. When sulfur is added to improve metal cutting performance, the surface quality is thus degraded. Steels with high sulfur content also become more brittle.

14 frequently asked questions in the field of mold manufacturing [on]

    (2) What are the primary factors affecting the machinability of materials?

    The chemical composition of steel is very important. The higher the alloy composition of steel, the harder it is to process. As the carbon content increases, the metal cutting performance decreases.

    The structure of the steel is also very important for metal cutting performance. Different structures include: forged, cast, extruded, rolled and machined. Forgings and castings have very difficult to machine surfaces.

    Hardness is an important factor affecting the metal cutting performance. The general rule is that the harder the steel, the harder it is to process. High speed steel (HSS) can be used to process materials up to 330-400HB; high speed steel + titanium nitride (TiN) coatings can process materials up to 45HRC; for materials with hardness 65-70HRC, Carbide, ceramic, cermet and cubic boron nitride (CBN) are used.

    Non-metallic inclusions generally have an adverse effect on tool life. For example, Al2O3 (alumina), which is a pure ceramic, has a strong abrasiveness.

    The last one is residual stress, which can cause metal cutting performance problems. It is often recommended to perform a stress relief process after roughing.

    (3) What are the production costs of mold manufacturing?

    Roughly speaking, the distribution of costs is as follows:

    Cutting 65%

    Workpiece material 20%

    Heat treatment 5%

    Assembly / adjustment 10%

    This also clearly demonstrates the importance of good metal cutting performance and excellent overall cutting solutions for the economic production of molds.

    (4) What is the cutting characteristics of cast iron?

    In general, it is:

    The higher the hardness and strength of cast iron, the lower the metal cutting performance and the lower the life expectancy from the blade and tool. Cast iron used in metal cutting production generally has good metal cutting performance. Metal cutting performance is related to structure, and harder pearlitic cast iron is more difficult to process. Flake graphite cast iron and malleable cast iron have excellent cutting properties, while ductile iron is quite bad.

    The main types of wear encountered when machining cast iron are: abrasion, bonding and diffusion wear. Abrasive is mainly produced by carbides, sand inclusions and hard cast skin. Bond wear with built-up edge occurs at low cutting temperatures and cutting speeds. The ferrite portion of cast iron is the easiest to weld to the insert, but this can be overcome by increasing the cutting speed and temperature.

    On the other hand, diffusion wear is temperature dependent and occurs at high cutting speeds, especially when using high strength cast iron grades. These grades have high resistance to deformation and result in high temperatures. This wear is related to the interaction between the cast iron and the tool, which allows some cast irons to be machined at high speeds using ceramic or cubic boron nitride (CBN) tools for good tool life and surface quality.

    Typical tool properties required for machining cast iron are: high heat hardness and chemical stability, but also related to process, workpiece and cutting conditions; the cutting edge is required to have toughness, heat fatigue wear and edge strength. The degree of satisfaction with cutting cast iron depends on how the wear of the cutting edge develops: rapid bluntness means hot cracks and gaps that cause premature cutting of the cutting edge, damage to the workpiece, poor surface quality, excessive waviness, and the like.

    Normal flank wear, balance and sharp cutting edges are just what you need to do.

    (5) What are the main and common processing steps in mold manufacturing?

    The cutting process should be divided into at least 3 process types:

    Roughing, semi-finishing and finishing, and sometimes even super finishing (mostly high-speed cutting applications). The residual milling is of course prepared for finishing after the semi-finishing process. It is important to work hard in each process to leave a uniform distribution of allowance for the next process.

    If the direction of the tool path and the workload are rarely changed rapidly, the tool life may be extended and more predictable. If possible, the finishing process should be performed on a dedicated machine. This will increase the geometric accuracy and quality of the mold during shorter commissioning and assembly times.

    (6) Which tool should be mainly used in these different processes?

    Roughing process: round insert milling cutter, ball end mill and end mill with round nose radius.

    Semi-finishing process: round insert milling cutter (round insert milling cutter with diameter range of 10-25mm), ball end mill.

    Finishing process: round insert milling cutter, ball end mill.

    Residual milling process: round insert milling cutter, ball end mill, vertical mill.

    It is important to optimize the cutting process by selecting a specific combination of tool size, geometry and grade, as well as cutting parameters and appropriate milling strategies.

    For the high-productivity tools that can be used, see Mold Making Sample C-1102:1

    (7) Is there one of the most important factors in the cutting process?

    One of the most important goals in the cutting process is to create an evenly distributed machining allowance for each tool in each process. This means that tools of different diameters (from large to small) must be used, especially in roughing and semi-finishing operations. The primary criterion at all times should be as close as possible to the final shape of the mold in each process.

    Providing a uniform distribution of machining allowance for each tool guarantees constant and high productivity and a safe cutting process. When ap/ae (axial cutting depth/radial cutting depth) is constant, the cutting speed and feed rate can also be constantly maintained at a high level. In this way, the mechanical action and the workload change on the cutting edge are small, so that less heat and fatigue are generated, thereby increasing the tool life. If the latter process is a semi-finishing process, especially for all finishing processes, unmanned or partially unprocessed. Constant material machining allowance is also the basic standard for high speed cutting applications.

    Another advantageous effect of a constant machining allowance is the small adverse effect on the machine tool, the guide rails, the ball screw and the spindle bearings.

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14 frequently asked questions in the field of mold manufacturing [2]

Core Tips: 8. Why do you most often use round insert milling cutters as the first choice for mold roughing tools? If a square shoulder milling cutter is used for rough milling of the cavity, a large amount of stepped cutting allowance is removed in the semi-finishing process. This will cause the cutting force to change and the tool to bend. The result is an uneven machining allowance for the finishing process, which affects the geometric accuracy of the mold.

 8. Why do you most often use round insert milling cutters as the first choice for mold roughing tools?

    If a square shoulder milling cutter is used for rough milling of the cavity, a large amount of stepped cutting allowance is removed in the semi-finishing process. This will cause the cutting force to change and the tool to bend. The result is an uneven machining allowance for the finishing process, which affects the geometric accuracy of the mold.

    If a square shoulder cutter with a weaker tip (with a triangular blade) is used, an unpredictable cutting effect can result. Triangular or diamond-shaped inserts also produce greater radial cutting forces, and because of the small number of cutting edges, they are less economical roughing tools.

    On the other hand, round inserts can be milled in a variety of materials and in all directions. If used, smooth transitions between adjacent passes can also result in smaller and more uniform processing for semi-finishing. margin. One of the characteristics of round inserts is that the chip thickness they produce is variable. This allows them to use a higher feed rate than most other blades.

    The main blade of the circular blade changes from almost zero (very shallow cutting) to 90 degrees, and the cutting action is very smooth. At the maximum depth of the cut, the lead angle is 45 degrees, and when cutting along a straight wall with an outer circle, the lead angle is 90 degrees.

    This also explains why the strength of the circular insert tool is large - the cutting load is gradually increasing. Roughing and semi-roughing should always be the first choice for round insert milling cutters such as CoroMill 200 (see mould manufacturing sample C-1102:1). In 5-axis cutting, the round insert is very suitable, especially without any restrictions.

    By using good programming, round insert milling cutters can largely replace ball end mills. The combination of a circular blade with a small amount of runout, combined with a finely ground, positive rake and light cutting geometry, can also be used for semi-finishing and some finishing operations.

    9. What is the effective cutting speed (ve) and why it is always very important to calculate the effective cutting speed on a high productivity diameter.

    Since the table feed depends on the speed at a certain cutting speed, if the effective speed is not calculated, the table feed will be calculated incorrectly.

    If the tool's nominal diameter value (Dc) is used in calculating the cutting speed, the effective or actual cutting speed is much lower than the calculated speed when the cutting depth is shallow. Such as round insert CoroMill200 tools (especially in the small diameter range), ball end mills, large nose arc end mills and CoroMill390 end mills (see the mold manufacturing of Sandvik Coromant for these tools) Sample C-1102: 1).

    As a result, the calculated feed rate is also much lower, which severely reduces productivity. More importantly, the cutting conditions of the tool are lower than its capabilities and recommended application range.

    When performing 3D cutting, the diameter at the time of cutting is varied, which is related to the geometry of the mold. One solution to this problem is to define the steep wall area of the mold and the shallow area of the part. Good compromises and results can be achieved if specialized CAM procedures and cutting parameters are programmed for each zone.

    10. What are the important application parameters for successful hardened die steel milling?

    When finishing high-speed milling of hardened die steel, one of the main factors to be observed is shallow cutting. The depth of cut should not exceed 0.2/0.2mm (ap/ae: axial depth of cut / radial depth of cut). This is to avoid excessive bending of the tool holder/cutting tool and to maintain a small tolerance and high precision of the machined tool.

    It is also important to choose a very rigid clamping system and tool. When using solid carbide tools, it is important to use tools with the largest core diameter (maximum flexural rigidity). A rule of thumb is that if the diameter of the tool is increased by 20%, for example from 10mm to 12mm, the bending of the tool will be reduced by 50%.

    It can also be said that if the tool overhang/extension is shortened by 20%, the bending of the tool will be reduced by 50%. Large diameter and tapered shanks further increase stiffness. When using ball end mills with indexable inserts (see mold manufacturing sample C-1102:1), if the shank is made of solid carbide, the bending rigidity can be increased by 3-4 times.

    When finishing hardened die steel with high speed milling, it is also important to choose a special geometry and grade. It is also important to choose a coating with a high heat hardness like TiAlN.

    11. When should I use down-cutting and when should I use up-cut milling?

    The main recommendation is to use as much milling as possible.

    When the cutting edge is just cutting, the chip thickness can reach its maximum value in the down-cut milling. In the case of up-cut milling, it is the minimum value. In general, tool life in up-cut milling is shorter than in down-cut milling because the heat generated in up-cut milling is significantly higher than in down-cut milling. When the chip thickness is increased from zero to maximum in up-cut milling, more heat is generated because the cutting edge is subjected to a higher friction than in the down-milling. The radial force is also significantly higher in up-cut milling, which has an adverse effect on the spindle bearings.

    In down-cut milling, the cutting edge is mainly subjected to compressive stress, which is much more advantageous for cemented carbide or solid carbide tools than for the tensile forces generated in up-cut milling. of course there are exceptions. When using a solid carbide end mill (see tool in Mold C-1102:1) for side milling (finishing), especially in hardened materials, up-cut milling is preferred.

    This makes it easier to obtain wall straightness with a smaller tolerance and a better 90 degree angle. If there is a misalignment between the different axial passes, the tool marks are also very small. This is mainly due to the direction of the cutting force. If a very sharp cutting edge is used in the cutting, the cutting force tends to "pull" the knife toward the material. Another example of the use of up-cut milling is the use of old-fashioned manual milling machines for milling, where the screw of the old-fashioned milling machine has a large gap. Up-cut milling produces a cutting force that eliminates the gap, making the milling movement smoother.

    12. Copy milling or contour cutting?

    In pocket milling, the best way to ensure a successful path to a milling tool is to use a contour milling path.

    Milling cutters (eg ball end mills, see Mold Making Sample C-1102:1) Milling of the outer circle along the contour often results in high productivity because more teeth are being cut on larger tool diameters. . If the spindle speed of the machine is limited, contour milling will help maintain cutting speed and feed rate.

    With this tool path, the change in workload and direction is also small. This is especially important in high speed milling applications and in hardened material processing. This is because if the cutting speed and the feed rate are high, the cutting edge and the cutting process are more susceptible to the adverse effects of changes in the workload and direction, and changes in the working load and direction cause changes in the cutting force and the bending of the tool. Profiling along the steep wall should be avoided as much as possible. When copy milling, the chip thickness at low cutting speed is large.

    In the center of the ball-end knife, there is a danger of the blade being broken. If the control is poor, or the machine has no read-ahead function, it cannot be decelerated quickly enough, and the risk of chipping at the center is most likely to occur. The upper profile milling along the steep wall is better for the cutting process because the chip thickness is at its maximum at favorable chip speeds.

    In order to achieve the longest tool life, the cutting edge should be kept in continuous cutting for as long as possible during the milling process. If the tool enters and exits too frequently, the tool life will be significantly shortened.

This will exacerbate thermal stress and thermal fatigue on the cutting edge. It is more advantageous for modern carbide tools to have uniform and high temperatures in the cutting area than to have large fluctuations. The profiling milling path is often a mixture of up-cut and down-cut (zigzag), which means that the knife is frequently eaten and retracted during cutting. This tool path also has a bad influence on the quality of the mold.

    Each time a knife is used, it means that the tool is bent and there is a mark on the surface. When the tool exits, the cutting force and the bending of the tool are reduced, and there is a slight material "overcutting" in the exit portion.

    13. Why do some milling cutters have different pitches?

    Milling cutters are multi-edge cutting tools, the number of teeth (z) is changeable, and there are several factors that can help determine the pitch or number of teeth for different machining types.

    Materials, workpiece dimensions, overall stability, overhang dimensions, surface quality requirements, and available power are processing-related factors. Tool-related factors include enough feed per tooth, at least two teeth at the same time, and the chip capacity of the tool, which are only a small part of it.

    The pitch (u) of the milling cutter is the distance from the point on the cutting edge of the insert to the same point on the next cutting edge. Milling cutters are divided into sparse, dense and ultra-tight pitch milling cutters. Most of the Coromant milling cutters have these three options. See mold manufacturing sample C-1102:1. The dense pitch means that there are more teeth and proper chip space, which can be cut with high metal removal rate. Generally used for medium load milling of cast iron and steel. The fine pitch is the first choice for general purpose milling cutters and is recommended for mixed production.

    The sparse pitch means that there are fewer teeth and a large chip space on the circumference of the milling cutter. Spacing is often used for roughing to finishing of steel. Vibration in steel processing has a great influence on the processing results. Spalling is a truly effective solution to problems. It is the first choice for long overhang milling, low power machines or other applications where cutting forces must be reduced.

    The ultra-precision tool has a very small chip space and can be fed with a higher table. These tools are suitable for cutting of interrupted cast iron surfaces, cast iron roughing and small residual machining of steel, such as side milling. They are also suitable for applications where low cutting speeds must be maintained. Milling cutters can also have uniform or unequal pitches. The latter refers to the unequal spacing of the teeth on the tool, which is also an effective way to solve the vibration problem.

    When there is a vibration problem, it is recommended to use a toothless unequal pitch milling cutter as much as possible. Since there are fewer blades, the possibility of increased vibration is small. Small tool diameters can also improve this situation. A combination of well-adapted troughs and grades should be used ¨C a combination of sharp cutting edges and toughness.

    14. How to position the milling cutter for optimum performance?

    The cutting length is affected by the position of the milling cutter. Tool life is often related to the length of cutting that the cutting edge must bear. The milling cutter positioned in the center of the workpiece has a short cutting length. If the milling cutter is offset from the center line in either direction, the cutting arc is long.

    Keep in mind how the cutting force works and must achieve a compromise. With the tool positioned at the center of the workpiece, the direction of the radial cutting force changes as the cutting edge of the blade enters or exits the cutting. The gap in the machine tool spindle also exacerbates the vibration, causing the blade to vibrate.

    By deviating the tool from the center, a constant and favorable cutting force direction is obtained. The longer the overhang, the more important it is to overcome all possible vibrations.

    Another advantageous effect of a constant machining allowance is the small adverse effect on the machine tool, the guide rails, the ball screw and the spindle bearings.

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What should I do if there are dents in plastic products? These tricks for your reference

First, the cause of the dent

1, the thickness of each part of the product is different

2, the mold is under pressure

3, mold cooling is not enough

4. Deformation due to insufficient cooling time

Second, the associated knowledge

1. In the process of producing products, the dent is the most frequent occurrence of the bad phenomenon. The plastic injected into the mold shrinks when it cools. The early cooling part is the first hardened surface, and the inside will generate bubbles. The so-called dent is cooling. The slow portion produces a conspicuous concave surface in the direction in which the bubble contracts.

2. Materials with large shrinkage are also prone to dents. When the molding conditions are to be changed to eliminate the dents, the setting conditions should be set in a direction in which the shrinkage is small. That is, the mold temperature, the barrel temperature are lowered, and the injection pressure is increased, but it should be noted that residual internal stress may be caused thereby.

3, because the dent is not conspicuous, so if it does not affect the appearance, there is a deliberately processed on the mold into a corrosive appearance, such as striate, granular and so on. Also, if the molding material is HIPS, it is also effective to lower the mold temperature to lower the finish. However, once these methods have dents, it is difficult to repair the polished products.

Third, the solution

1. Instant: Increase the injection pressure, extend the injection pressure holding time, reduce the barrel temperature and mold temperature, and force cooling in the place where the dent is generated.

2, short-term: fill the flow edge where the dent is created. When there is a narrow place on the side of the material where the dent is generated, the side is thick.

3. Long-term: The difference in thickness of the design product should be completely avoided. Ribs that are prone to dents should be as short as possible.

Fourth, the difference in materials

A material with a large mold shrinkage has a large dent. For example, PE and PP produce dents even with a slight rib.

Material molding shrinkage

PS0.002~0.006

PP0.01~0.02

PE0.02~0.05

V. References:

1. When the temperature is lowered to no dent, if there is pressure in the material in the cavity, it should be considered that no dents will occur. The pressure within the mold, ie, the static pressure, of the material surrounding the mold is not necessarily anywhere. The pressure near the gate is high. If the material is wide, because the pressure to the corners is transmitted, the pressure difference between the near gate and the gate is not much different from the pressure of the whole. It is also possible to obtain a product which does not leave internal stress. When part of the material flows into a difficult place, there is a high pressure in this place, and the pressure in other places is lowered to cause dents. This part of the high pressure residue is also the internal stress of the product. In the ideal state, the temperature of the material rises with the temperature of the mold, the fluidity of the material is good, and the injection also changes to the bottom in the static pressure state.

2. When changing the molding conditions, the combination of temperature, pressure and time should be prepared in advance and in order, the results can be known early. First, after the time has become very long, it is easy to know the small changes in the pressure. It should be noted that the result when the temperature is changed should be the result after the injection of the material, and then the temperature is lowered and then produced.

The above content is How to control the color difference of injection products. I hope it will help you!