In the mechanical process, flash and burrs are molding defects that generate after processing. They can affect product quality and cost. It means the appearance of debris on the plastic molded parts is flash and burrs defects. A large number of flash and burrs on plastic parts means the low quality of products. They’re very common issues and have different names such as flash, burrs, and spew. Flash and burrs are challenges for the technicians in the plastic molding process. Some industries need deflashing and deburring products. Such as medical, marine, automotive, aerospace, and electronics. Flashing is excess material that attaches to the molded parts. It occurs due to the leakage of material between the surfaces of the mold. We can improve the plastic molding flash/burrs by cutting, breaking, and tumbling. It’s known as deflashing. Here we’ll discuss what’s flash? Why it occurs, and improve the plastic injection molding flash?
Some Steps For The Improvement Of Flash/Burrs
Flashing of parts occurs for various reasons. Flash may appear on the edge of parts with the parting line. It also happens anywhere where leakage of metal can make possible. The intensity of the flash depends on the type of product. The flash will not remove the parts that have a high tolerance. A related condition is witness lines or witness marks. You may find witness marks along the parting lines between the plates.
You can follow some steps to improve the flash and can reduce the mold damage. It is necessary to recognize the type of flash and what time it appears? It will help remove the defect and injection mold flaws issues.
1:Slow Down The Injection Rate
You can reduce flash injection molding by slowing down the injection rate. It can end the flash and burrs as it raises the viscosity of the material and cycle time. But it can’t completely root out the flash. Flash may appear during the packing step or the filling stage. You can see flash with thin-walled parts and conventional parts. By minimizing the pressure in the packing, the stage may reduce the flash. It should be less than 500 psi plastic pressure.
At the first step, injection fills at least 92% to 99.9% of the parts. It should finish till the fulfilling of the cavity. Minimal pressure proves effective for the inspection of the short shot at the first step. If you find flash on the short shot, give attention to parameters. That can affect first stage injection. If the shot doesn’t appear at all, you can adjust the transfer point. It prevents the overfilling of the cavity.
2: Clean Off All Dirt And Plastic For Improving Flash
Short shorts with a thin wall can generate ample pressure for blowing the clamp open. A parting line of mismatch in the mold tool may be flashing in part with average wall thickness. You must clean mold from any plastic, dirt, and contaminant. It can be problematic for the full closure of mold. Mold should check with great intention and care. Behind slides or in the pocket pins, plastic may locate. If flash appears, you can check part line mismatch with pressure-sensitive paper. It can identify the clamping of the mold with the parting lines.
An improper balance of molten flow is one of the reasons for flash in the multi-cavity. Imbalance filling leads to imbalance packing. This is the reason for flash on one cavity and sinks marks during the same shot. There’re many methods for the determination of mold balance. Lack of mold support is also responsible for flash. So you must know the injection molding machines have support for the cavity and core plates. Another source of flash is the sprue bushing.
3: Checking Of Clamp
Too little clamp tonnage is also a cause of flash. This type of flash can remove by increasing clamp tonnage. You may need 35,000 to 60,000 psi plastic pressure in the nozzle area. It will be a high-speed filling process in a thin-walled usage. If the machine is not on the proper level, the flash also occurs. Flash molding defects due to clamp misalignment can improve with a little effort. A new laser method is one of the recommended but costly methods. Injection molding companies use this method for checking the lack of clamp parallelism. Too high clamp pressure produces flash and burrs towards the center of the mold.
What Are The Causes Of Flash Defect In Injection Molding And What Are Its Remedies?
1: Old Mold
Old mold is the cause of creating a flash on the part surface. It doesn’t fit tight together, and plastic escapes out due to this looseness. Old mold or worn-out mold issues can solve with mold repairing or mold redesigning.
2: An Improper Balance Of Mold Flow & Pressure
Temperature, pressure, and flow are some common causes of flash and sprew. The packing will not be uniform if cavity filling is not uniform. This type of flash can improve by using the Beaumount five steps process.
3: Mold Clamping Issues
Very high clamp pressure and very low clamp tonnage also causes flash/burrs. The plate doesn’t clamp with enough force because it avoids the resin forces. It can solve by reducing hold pressure and with the usage of a press with high clamp force.
4: Mold Damage Problems
Parting lines mismatch and any obstruction in the proper clamping can resolve. Clean the mold surface and slides for this problem. You should also check mold tool damage, misalignments of the clamp, and machine level. With the help of pressure-sensitive paper, you can check and solve these problems.
5: Mold Design Issue
Poor design mold and having too much space also create pressure or flash issues on the part surface. It happens due to complex geometries and many parts. You can resolve this issue by retooling and redesigning of mold.
6: Too Low Viscosity Problems
Flashing or burring can create if viscosity pressure will be too low. In this issue, the resin becomes too runny. Some reasons for becoming resin too runny are:
- 1:The presence of moisture due to improper dryness
- 2:Excess amount of colorant consisting of lubricant vehicle
- 3:High melting temperature
- 4:Excess time of residence that creates degradation.
You can test melt temperature and melt flow. It will be according to the supplier’s instructions. Injection molding companies check temperature and mold flow in the molding process. For unfilling resin, you can change a 30% change in melt flow. For filled resin, you also change melt flow at least 40% or more.
What Is Meant By Deflashing And Deburring Methods?
Deflashing and deburring are the main steps in the plastic injection mold process. Product cost can increase after deflashing and deburring. Its cost depends on the size of parts, type of material and parts, and the product’s precision. Deflashing is a process of removal of unwanted parting lines. It removes the residue and debris leftover in a molding or casting process.
Deburring is a method of finishing and smoothing the edge. It occurs after the cutting and welding procedure.
Industries That Need Deflashing:
- Blow Molding
- Transfer Molding
- Spin Casting
- Injection Molding
- Compression Molding
- Thermoforming Industry
- Extrusion Molding
- Thermoforming
- Laminating Industry
- Reaction Injection Molding
- Matrix Molding
- Powder Metallurgy
- Rotomolding
Material Injection Molding Company Use In Deburring And De flash Procedure:
- Silicone
- Sheet Metal
- Nylon
- Polycarbonates
- Peek
- Polyurethanes
- Acetals
- ABS & Delrin
- Turcite & Ryton
- Synthetic Rubber
- PBT & Acetal
- Liquid Crystal Polymer
- Nitinol & Rubber
- Stainless Steel
- Aluminum
Media blast technologies use for many deflashing and deburring applications. Plastic beads blasting, steel shot blasting, sandblasting also include media blasting. Ice blasting is also one of the eco-friendly and cost-effective methods. Deflashing and deburring can perform by hand. Cryogenic deflashing use for producing great precision. Mechanical or automated deburring performs through an auto grinder and tumbler. All these methods are time-consuming and may cost you more for product production. Choose the best injection molding manufacturing company. That can provide you defect-free and cost-effective products.
What Are The Causes Of Bubbles And How You Can Prevent Bubbles In Plastic Injection Molding?
Bubbles are the major cause of cosmetic rejection in plastic molded parts. Bubbling is a very costly and time-consuming defect. Poor melt flow is one of the main causes, and you need to change the gate location to promote uniform filling. Bubble causes by two main reasons. One is a vacuum void, and the other is gas pockets. Before trying to solve these issues. It’s important to know which type of bubbles you’re facing and the main reason for it?
You can check the type of bubbles in plastic injection molding with a simple heat test. Warm the part area that affects by bubbles. Bubble shape will change after warming. If it expands and warm-up and the surface raises, it will be a gas pocket. If you don’t see any air in the bubbles and it collapses, it will be a vacuum void.
A gas pocket occurs due to flow front issues like jetting, and resin degradation. You can resolve these bubbles by adjusting hold pressure down.
The second stage test requires controlled velocity. It should need for the first stage. Otherwise, you can’t get an accurate result. In the second stage, make a part 99% full volume and decrease the size from 99% to 5% with the increment of 10%.
Check the flow pattern and the area of the bubbles. Do they appear at the same place? It means they’re coming from the same and fixed area. If you see bubbles appear after the 85% filling, it may be a venting problem. There are many ways for the sucking of air into the melt flow. Such as nozzle misalignment, and ribs ejector pins. One solution is to pull a vacuum on the molded part. It will do before the injection molding and air pulls out.
Void creates in the cooling procedure when your part is outside and inside the mold or thick areas. The centers cool with slow speed in the thick section and form a bubble. By running the mould hotter, if the bubble removes and finds a sink mark, it will be a void defect. Sink marks develop in the thick area during the finished products’ shrinkage. Lack of plastic is the main reason for creating a void. So you should pack more material into the mold cavity. Long holding time and high hold pressure may be useful in this regard. To get rid of the void and sink mark, you can increase back pressure and slow the filling rates. Reducing the melt temperature also proves beneficial for the removal of void/sinks.
Conclusion
A good injection molding company aims to provide high-quality parts to its customers. But some shortcomings associate with the injection molding process. These flaws solve if your selected company has full knowledge of troubleshooting. It knows the creation of tools and the process of plastic injection molding. Thus choose a certified and qualified company for your project. The company that can improve the flash/burrs in the plastic injection molding process.
