7: Injection Mold Making

Plastic Injection Mold making in China

 
Once the shape of the plastic and metal parts is frozen we make the steel molds used to mass produce the housing and other parts. Our local engineers discuss the mold drawings with the Chinese mold makers to assure the robustness and the aesthetic quality of the parts. Mold making in China tends to be a lot more affordable than in the West, and a lot faster as well, with first shots often ready in 5 weeks.

 
It’s hard for one mold maker to be good at everything, so over the years we have built up a roster of specialised shops for precision molds like cosmetic parts, optical lenses, gears, metal brackets anddie-cast parts.. When all these custom parts come together in an complex electro-mechanical assembly a lot of tiny adjustments are needed and every iteration comes with a negotiation.To make sure the project does not lose momentum our engineers stay at the mold shops until the job is done properly.

(Extra tekst; brontekst http://www.titoma.com/molds-parts.php)

 

What is an injection mold?

 
A mold is a hollowed-out block of steel that is injected with molten material such as plastic, which then hardens to take on the counterpart shape of the mold. An injection mold is necessary when an electronic project requires a custom plastic or metal housing.

 

What are injection molds made of?

 
Molds are made from a variety of steels. Examples of some common steels used in plastic injection include P20, NAK80, H13, and S7. Each vary in terms of hardness, wear resistance, compression strength, corrosion resistance, machining ease, polishability, weldability

 

What are the cost considerations of injection molds?

 
China is well known for its unprecedented value for money with regards to mold making, yet some businesses choose Western- over Chinese moldmakers, assuming the quality of the steel improves the endurance of the mold result, resulting in a lower percentage of the costs.
Choosing for a higher quality steel might constitute to a lower percentage of the costs when made by western mold makers, yet this is only due to the high labor costs. In fact, plastic enclosure is the cost component on which you can realize the largest cost difference between Asia and the West.
From our experience it makes financial sense to invest in a mold at quantities of 250 pieces and up. And once you have invested in molds, the more you produce the more you save.

 

What are the challenges of plastic injection mold?

 
Injection molding is an art in itself. A good mold design will increase the chance of getting well-molded enclosures and parts, yet it is also essential to use the correct plastic injection parameters appropriate to the parts being produced and material used; otherwise the parts may come out defective.
 
Common Molded Part Defects:
 

  • Burn Marks: Burnt areas at furthest points from injection gate caused by an injection speed that is too high so the mold lacks venting
  • Flash: Excess material caused by a too high injection speed/material injected, a damaged parting line or a too low clamping force.
  • Flow marks: Wavy lines or patterns caused by an injection speed that is too slow
  • Knit lines: Small lines on parts caused by the plastic flowing around an object; can be minimized or eliminated with a mold-flow analysis.
  • Sink marks: Depressions caused by either a pressure that is too low; cooling time too short; or enclosure walls mthat are too thick
  • Short shot: Incomplete parts caused by an injection speed or pressure that is too low
  • Splay marks: Lines/Marks caused by gas or moisture flowing along the part during injection process
  • Warping: Warped part caused by a cooling time that is too short or material that is too hot

 

 

What types of plastic injected enclosures (housing) can you choose from and why?

 

 

Plastic enclosures

Custom plastic enclosures give your electronic products the greatest freedom in shape and the lowest cost per unit.

 

PC(Polycarbonate)

has excellent impact strength, clarity, and optical properties and can be molded to tight tolerances. Its disadvantages are its subjection to stress cracking and/or yellowing after long time.

 

ABS(Acrylonitrile Butadiene Styrene)

ABS plastic has good mechanical toughness, dimensional stability, chemical resistance, and ease of fabrication. Its disadvantages are its poor solvent resistance and it melts easily.

 

PP(Polypropylene)

Polypropylene is widely used and inexpensive but is difficult to mold to precision. Its disadvantage is its degradation caused by UV

 

Metal Enclosures

Plastic is often the most cost effective option for production in large quantities, but a metal enclosure will give your device a high-end quality look and feel. A custom metal enclosure made in China or Taiwan can become cost effective at quantities as low as 200 pieces. Our partners can develop fast turn-around milled (CNC) metal enclosures at reasonable prices. Once you get to quantities of 500 units, you can significantly lower the unit cost by going for a stamped metal housing produced using a progressive die. Alternatively, to get more freedom of form you could go for die-cast housings in zinc or magnesium.

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Phil Baker - US Representative for Titoma Product Development in China

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546 Canyon Drive, Solana Beach, CA 92075 USA
author of “From Concept to Consumer: How to Turn Ideas Into Money”

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