Injection molding is one of the key business areas of Topworks Plastic Molding, and the Injection molding department primarily focuses on injection molding and secondary operations.
It is aimed at enhancing product quality, improving production efficiency, and controlling manufacturing costs.
The company possesses the latest mold maintenance technology, nitrogen molding technology and automated high-end production technology.
The company installs 30 injection molding machines from Toshiba and Haiti, with tonnage ranging from 40T to 1300T, in order to ensure quality of products and to boost production capacity.
- Various types of injection molding machines are available to meet the requirements of different customers.
- Our team has years of experience in the injection molding industry and we are good at it. We specialize in all kinds of electronic appliances, and also household appliances and industrial products.
- We have been involved in various types of plastic engineering, including horizontal injection molding, vertical injection molding, and overmolding;
- Stability of product quality is ensured by the standard operation;
- Continuously improve production efficiency;
- I believe that we understand the different needs of customers and we can provide them with high-quality products that exceed their expectations.
- Spray: PU paint, rubber paint, UV paint, high gloss paint, leather, metal paint, etc..;
- Printing: screen printing;
- Laser carving, plating, heat transfer, silk transfer;
- Hot melt, ultrasonic welding.
The plastic material we usually use:
- ABS(with glass fill)
- Polypropylene(with glass fill)
- Nylon(with glass fill)
- PBT(with glass fill)
- PC(with glass fill)
What information is needed for injection molding?
The following are the items included in the calculation of actual injection molding manufacturing costs. Injection molding is deemed a primary manufacturing process.
- Materials and labor costs
- Raw material in a project.
- Recycled substance
- Allowances for scrap
- Estimated amount of regrind buildup
- Labour, direct and indirect
- Timed versus non-timed
- Rate (hourly) for machine
- Setup fees
- Downtime allowances and scrap allowances
- Mold cavity count
What behind the plastic injection molding price
The price of a plastic part will depend on factors such as the price of raw materials, labor,packaging and setup costs.
it’s not difficult to determine the cost of these factors because they are known and can be calculated before the project begins
However there are two factors that make pricing a plastic part difficult and that cause the greatest difference in pricing between competitors.
They are estimated press cycle time and estimated part weight.
These two factors are difficult to calculate because they are unknowns.
A company will only have to estimate cycle time and part weight until a sample part is made.
Companies estimate the part price by using the experiences they have had making similar parts.After the sample part is made, a company can give an accurate price for the part.
Let’s go through an example using a blueprint or part drawing, the engineer will calculate the part volume then by
using the specific gravity of the specified plastic they will determine the part weight.
The cost per pound to purchase.
The raw material is applied to the part weight and the cost of plastic ,and part is calculated then the engineer estimates the cycle time in the molding cycle using his or her experience applying the number of cavities in the mold and the cost of labor and press per hour， the labor charge is calculated.
Each order will have a minimum set up charge spread over the quoted quantities.Other additions such as secondary
operations packaging and sales commissions may be added to the price.
The price for a part would be represented in different quantity breaks because of the set-up cost and sometimes because of the change in the cost of raw material given larger quantities.
if you would like to compare pricing from several moulders ,be sure to ask the moulders to disclose the cost per pound of raw material, number of cavities in the mold ,estimated cycle times and estimated part weight.
You can create a spreadsheet to compare all the information a molder that will not provide details in their quotations
should raise questions in your mind.
Keep in mind that the low bidder may not always be the best, be sure to ask for a price guarantee.
injection moulding process
Injection molding is a complex process that involves an injection of a polymer into a mold where it is shaped into the desired shape. This process consists of four stages. These stages are clamping, injecting, cooling and ejecting.
The mold has to be closed prior to injection ,before the material can flow. It is closed by means of a clamp unit. Both halves are then attached to the injection molder and one of them can be slid.
When the mold has been closed, it is clamped by the clamping unit by which the halves are kept tightly together. It takes longer for larger machines to close molds that have more clamping power, so in most cases it will take slightly longer to close a mold as well.
Plastic pellets are fed into the injection molding machine through a large hopper. These pellets pass into the injection unit, which mixes them with the surrounding heat and pressurized air. The temperature of the surrounding barrel and the pressure help to melt the pellets.
The injection time of plastic is measured by the volume of material injected and is calculated when 95%-98% of the mold is filled. Getting the injection process exact is difficult because the flow of plastic is constantly changing and dynamic.
Other factors such as injection pressure and injection power can also be used to estimate the injection time. An injection pressure meter can measure from 35-140 MPa. An injection time and the maximum pressure will be predicted and controlled by the hydraulic system in the machine.
After the plastic inside the mold starts to cool and harden, it will form the desired shape. During the cooling process, the plastic may shrink slightly. Only after this time period has passed, can the mold be opened.
The cooling time of the part can be determined by understanding its wall thickness and the thermodynamic properties of the plastic.
When the mold opens, the part is pushed out utilizing force as the part shrinks and will stick to the mold. After the mold is closed permanently, another injection can be made to re-start the process.
Mold design is a critical factor to ensure that the end product is of high quality.
The plastic mold has to be stable and capable of withstanding the pressures during the injection process. This is because the strength, durability, shape, and size all depend on the type of mold selected.
The polymer must also behave properly as it flows along the mold, and the mold must also be carefully designed to permit heat transfer that regulates the cooling process.
It is a complex operation requiring highly trained personnel to ensure the entire process is carried out. Keeping productivity high is imperative, and the safety of the workers is a primary concern as well.
Injection Molding Component Design
There are several basic concepts in component design which, if followed, will help to relieve many of the problems that beset the injection molder. Among these are:
- Maintain the wall thickness as uniform as possible.
Differences in thickness of only 15-25 percent will often lead to sink marks forming in the thicker parts.
At worst，voids could be produced and these could affect the performance.
Rigidity can often be imparted by introducing a stepped section (cf. corrugated roofing sheets), and even box sections are made more rigid while keeping their thickness even,by slightly rounding the corners.
If ribs and bosses are to be introduced, sink marks may occur and may be difficult to avoid.
A useful rule is to make ribs only two-thirds of the general wall thickness and to design bosses similarly, causing holes to penetrate one-third of the depth into the wall.
- The wall thickness should be no greater than is necessary to give the strength and rigidity needed.
This keeps the use of material to the minimum and provides the shortest possible time cycle- Careful use of multiple gating can probably solve problems of mold filling.
- Undercuts and re-entrant shapes cause extra costs both in mold production and in molding time (side core operation very often increases the time cycle)
They can often be avoided by the use of simple assembly methods applied to two or more components.
One of the most favored of these is the interference fit in which one component has a clip or other device which engages strongly with the other part and holds the two together (cf. the poppet bead).
Welding by friction，hot plate，or ultrasonic means can also be used, but in general,cementing with solvent or solvent-based adhesives is not recommended for the custom molder because of fire and toxicity hazards and problems of solvent recovery.
- Avoid the use of molded-in inserts if possible.
Use instead staked or spring-clip inserts into blind holes which are easier to make by injection molding.
Insert molding is often very wasteful of time,of both operator and machine, and this is generally the most expensive part of the process.
- Give the most generous radii possible.
Sharp corners, both external and internal,are natural stress-raisers but a radius of 0.06 in (1 -5 mm) will significantly relieve the situation and may increase impact strength by as much as five or ten times.
Component designers may call for something that is difficult to mold.
As the producer of a well-known brand of hand-tool manufacturers put it in an advertisement: “Occasionally, so rarely, in fact，that one feels rather guilty about mentioning it, designers have been known to create things which are just a teeny-weeny bit difficult to make.
Production men rejoice in challenges of this kind, of course,and the English language would be poorer without them. “The same could，perhaps, be said of the injection molder.
Designers may be working in a state of ignorance—ignorance of the service conditions of a component,ignorance of the service performance of a material, and ignorance of the many factors involved in proceeding from component design to complete plastic molding.
There is a need for education but, even more,there is a need for consultation and cooperation.
Regular liaison between end user,component designer,mold designer, and molding technologist will prevent many of these problems from arising.
Example of an approach to product design development:
1. Define the purpose and performance of the product.
2.Determine if the product has space and load limitations.
3. Define how the product will be exposed to environmental stresses during its intended function.
4. Choose two or three materials that appear to satisfy the environmental conditions and the strength requirements.
5. Perform several trials with different materials and geometries to evaluate their suitability for use in the application under consideration.
6. Conduct a thorough cost-effectiveness analysis of the trial designs. Determine different levels of performance and associated costs associated with each level of performance, as much as possible with the data available.
7.Determine the fabrication method that is most appropriate to the design.
8.With the preliminary assessment select the most logical alternatives and prepare a detailed design of the product.
9.Based on the detailed design of the final product, determine the probable design, the material, and the manufacturing process.
10. If required, construct a model for testing the product’s effectiveness.
11. Create prototypes.
12. Develop and test prototype products to determine if they serve the intended purpose.
13. Based on the prototype testing, the product should be redesigned.
14. Test again.
15. Field tests should be conducted.
16. Add instructions on how to use the software.
17. Design ready
Injection Molding Troubleshooting
1. Short shot:The plastic parts have irregular and incomplete edges. It usually occurs at the farthest point of the gate; the roots of thin and long ribs.
2, Shrinkage: Occasionally, a place: 1. when the material thickness is uneven, 2. thick section of injection molded part, 3. boss and rib section. Due to shrinkage, the plastic parts develop dent, uneven and it looks wavy under low light conditions.
3, Flash: A part edge with an extra thin layer of plastic is often found in the following locations: 1. Parting line; 2. Moving core; 3. Ejector pin position, boss position, hole position, snap location.
4. Bubbles: The bubbles on the surface of the plastic are of a different color from the surrounding colors and are typically: 1. bubbles caused by gas, air and water gas which is not released in time. 2. bubbles caused by shrinkage. The bubbles in the transparent part are particularly distinct.
5. Weld line: When multiple molten flow fronts coincide with each other, a deep weld mark appears on the surface of a plastic part. This most commonly occurs at the confluence of multiple molten flow fronts.
6, Burning : it is not a flat surface, it is usually dark or black spots, usually they are found in sections where it is difficult to fill and trap the gas easily.
7, Black spots: black impurities are evident on the surface of the plastic parts, mainly caused by the use of mixed materials.
8. Discoloration: The slight difference in color between the actual plastic part and its required color is very apparent, and it is generally because the pigment is incorrect, the mix ratio is incorrect, or the mold is set at a wrong temperature.
9. Wrinkles: The plastic parts show wavy lines on the surface that are caused by the cooling of the resin flowing.
10. Deformation: The plastic parts have distortions, undulations, curves, and this is particularly common in the bosses, ribs, and round-shaped injection parts. These are specially common to PP injection molding.
11. Wrong materials: In contrast to the specified materials, the one here can be identified by checking out the packaging label, the density, the burning continuity, the color of the flame, the color of the smoke, and the length of the flames.
12. Stick to the mold: Incomplete plastic part staying in the cavity, in contrast to short-shot, or due to the lack of designing the mold ejector system, the plastic part is hard to be ejected from the cavity, generally in thin-walled areas, bosses, and snaps.
13. Scratch:The surface of the plastic parts rub against the surface of the cavity during the ejection, so that a lot of them have scratches on the surface.
14, Over-flow: It is caused generally by cavity damage and occurs on the active section, bosses, ejector pins and parting surface.
Click for more information as to the injection molding troublshooting.