Is injection molding right for my project?

Injection molding is a very effective manufacturing method to get large quantities of high quality manufactured plastic products at a low unit cost. However there is a upfront cost of tooling that can be many thousands of dollars depending on part size and complexity of geometry.

Are there opportunities to reduce tooling cost?

Tooling cost can vary greatly depending on part geometry, cavities, and materials and automation in the tooling.  Yes, there are ways to tool up for low quantities and reduce up front tooling cost and lead-time.  The trade-off will usually be higher part cost due to low cavitation, lack of automation and increased secondary labor.

  1. Go with lower cavitation (less machining, smaller mold base)
  2. Eliminate any secondary automation in tooling such as slides, collapsible cores, and automated unscrewing operations to make a tool that is a straight open and close tool. You can still achieve the desired part geometry with hand loaded inserts or secondary machining cost.
  3. Master Unit Die set (MUD) – Your molding partner may have a set of Master Unit dies that allows you to eliminate the cost of a mold base. Essentially, you will cut core and cavities to fit into the master unit die.  These are generally used for smaller parts, but can help reduce cost and reduce lead time to production.  Typically all you will own are the cores and cavities so you may lose the flexibility to move the tooling to another vendor.
  4. Materials – Softer metals such as aluminum can speed up the fabrication process and save some manufacturing cost. The trade-off is materials that generally do not wear as well, are more susceptible to damage and can be more difficult to repair.
  5. Technology advancements – 3D printing of high heat or metal inserts are making their way into the market to reduce lead-times and machining cost. These materials are rapidly improving, but are more used for prototyping and “bridge to production” tooling.

How do I scale up to production cost effectively?

The strategy will be different for every product depending on the confidence of the market demand and consideration of utilization of capital investment.

  1. If you are under-capitalized or just testing the market you may want to start with fabrication. Fabrication can involve printing, machining, forming, gluing or other operations to get a few parts to test the market.
  2. If fabrication is too costly or the demand may outstrip the fabrication capability, you may want to invest in bridge to production tooling. This may also be the right strategy if you are short on capital or are uncertain about final part design.  This strategy will preserve some capital and give you greater production volumes.
  3. If you are fairly certain about the market demands and have the capital, you can proceed with production tooling. Take the time to weigh your options for automation in the tooling and cavitation.  In some cases it may make sense to invest in a tool with multiple cavity inserts and give you the flexibility to add cavities or make changes easier.

What is the best process for prototyping?

There are many factors that influence this decision.  It is best to research the various technologies once you have clearly defined what you need to learn from your prototype.  Some of the high level things to think of when evaluating prototype methods.

  1. Do you need it to test mechanical performance?
  2. Do you simply need it for pre-market sales and business development?
  3. What quantity will you require. Some methods are more suited for 1 -2  parts and some can be cost effective for hundreds.
  4. What production process will I use for manufacturing. You want to begin with the end in mind and develop your design and prototype with the end production process in mind to avoid developing a product that cannot be manufactured efficiently to meet your cost targets.

What is the best production process for my project?

There are many processes for processing plastic parts.  I will highlight the major characteristics of each to help with general guidance.

  1. Injection molding – Injection molding is the most common form and involves melting the plastic resin and injecting into a mold at high pressures. This process provides complex geometry, low part cost, higher volume capacity, many material options.  Due to the high pressures involved in the injection molding process the tooling cost is a significant investment.
  2. Blow molding – Involves extruding a tube of material that is captured in a mold and injected with air to push/blow the plastic resin to the walls of the mold. This process is commonly used to manufacture bottles, small jugs and other hollow parts like plastic footballs, duck decoys or any sort of hollow plastic product.
  3. Extrusion– Extrusion uses a screw to pump material through a die in the desired shape. Typical products for extrusion may be sheet, film, pipe, tubing, rod or profile shapes like used in manufacturing a window frame or shaped gasket.  These shapes are in a continuous length and can be cut to length or coiled.
  4. Fabrication – Parts can be fabricated from stock sheet and shapes of material. Sheet stock may be cut to size and welded or fastened together with mechanical fasteners.  Heat can be used to bend stock shapes such as rods and solvents and glues are also commonly used to build products.  The process is labor intensive and material is wasted in the process of using common sheet sizes.
  5. Casting – Casting is a low volume process that involves pouring a material into a mold and allow to cure. When the mold is opened the part can be removed, trimmed or any secondary operation that need to be completed to finish.  Urethane is a good material for casting because it is a tough material, can be colored and can create soft flexible parts to super hard parts.
  6. Thermoforming – Thermoforming is a common process for taking plastic film or sheet and heating the plastic until the point of softening. When the material is soft a tool is used to pull the plastic into the tool with the use of vacuum through small holes in the surface of the tool.  The design is limited to parts that can be vacuumed from a flat sheet into a formed surface.  Tooling cost is much less than injection molding and typical products made from thermoforming plastic film may be clam shell packaging products or disposable plastic cups.  Thermoforming of thicker gauge sheet is used for plastic sign faces, skylights and plastic lids for dumpsters.
  7. Rotational molding – For large parts plastic resin can rotated within a mold to coat the inside and when cooled can be removed from the mold to form products like kayaks, pontoons, and ice chests. The cycle for each part may be many minutes so daily production volumes are limited in comparison to processes like injection molding or blow molding.
  8. RIM molding – RIM (Reaction Injection Molding) uses two components that when injected into a mold will create a reaction that sets up the resin to form parts. RIM is useful in large parts as high pressures are not required so that equipment and tooling costs are less than would be in very large injection molded parts.  RIM is used to make a variety of parts from rubber like window gaskets to large cosmetic hoods for farm tractors.
  9. Foam Molding – Foam molding is another popular process for molding large parts. The plastic resin is injected into the mold and a foaming reaction causes the resin to fill the cavity before forming a skin and hardening.  Like RIM the internal pressures are lower than required in traditional injection molding the tooling cost is lower and can create large structural parts like enclosures for MRI machines, Frames and covers for gas pumps and ATM machines.

These are the major processes and there are many other methods to produce

What material do I use?

Know the performance requirements for the material:
What are the mechanical requirements?
Will it have high exposure to U.V. from the sun? 
Will it be exposed to any chemicals?
It is best to start from the commodity materials and work up than start with a popular branded product that may not meet your requirements and cost more.  A designer once advised me to always ask the question Why not HDPE or PP?

Should I produce in China or U.S.?

Be sure to factor in the total cost of ownership along with a factor for associated risks.  Generally you have much better legal protection of your Intellectual Property and better success in managing conflicts with suppliers in the U.S.  Certainly transportation costs to ship product from across the world is greater, but also consider the cost of time on the water as a longer lead time in your supply chain may require a greater investment in inventory.  If parts are large or do not package efficiently the increased shipping cost may eat up any piece cost savings.  Even with the best of U.S. and overseas suppliers defective product will eventually be part of the equation.  The cost to return, rework, time to replace and frustrations that are frequently associated with quality concerns are exponential with long distances and language barriers.  Certainly there are many instances when manufacturing overseas is the best option, just be careful to really consider all the costs.

What information do I need to get started with injection molding?

In order to provide an accurate quote the manufacturer will need a 3D model of the part typically in a common file format such as .stp or .igs.  Most companies can read these files and calculate part volume and weight.  You will also need to provide critical dimensions, tolerances, material specifications, packaging specification and quantity.  There are more details that may be required, but these are the basics to ensure you get accurate cost and get started with an injection molded project.  We also have a Design Guide that may be of assistance

Design Guide