Now you already have a plastic enclosure that has been validated by prototypes, and you need to make 100 parts for the next stage. You are not sure whether to choose 3D printing, vacuum casting, or injection molding.

Table 1: Comparing Process Options for 100 Parts

Why 3D printing, vacuum casting, and injection molding may all be considered for the same batch of 100 parts, and what to consider before choosing one.

So, when facing this situation, how should we choose? Let us ask ourselves these four questions one by one, and the answer will naturally become clear. In the following sections, “it” means this batch of 100 parts.

First, you need to ask yourself why you are making this batch of parts. We can use some concepts from the New Product Introduction (NPI) process to help us understand the current stage of these 100 parts.

NPI Validation Stages: EVT, DVT, and PVT

EVT, DVT, and PVT represent different validation objectives during new product introduction, helping determine what the next batch of parts needs to prove.

Image source: Encata, “Hardware Product Development Stages: POC–EVT–DVT–PVT Explained”

As the product becomes more mature, it usually goes through three stages: EVT, DVT, and PVT. The validation goal at each stage is different.

Why Does the Validation Goal Matter?

EVT, Engineering Validation Test, mainly validates whether the product concept and function work during the product development stage. The requirements for the parts/manufacturing are mainly fast production, prototypes, and small batches.

DVT, Design Validation Test, validates whether the appearance, performance, and reliability meet the requirements. Therefore, this batch of parts needs to be closer to the final design, material, and performance.

PVT, Production Validation Test, focuses on whether the factory can produce the parts efficiently, repeatedly, and consistently. In general, this means that production tooling is needed.

What Do You Need to Validate?

It is important to note that EVT, DVT, and PVT do not correspond one-to-one with 3D printing, vacuum casting, and injection molding. They are more useful for helping us understand “what exactly do these parts need to prove?” If we think about what this batch of parts is mainly for in this way, we can get a general answer in the first step.

Table 2: What Do You Need to Prove?

How different validation goals point toward different manufacturing processes for the next batch of parts.

Note: This only gives us an initial direction, not the final answer. We still need to answer the next three questions.

After deciding what you want to get from this batch of parts, the next question is whether your design is mature enough. From an engineering point of view, this question can be more accurately written as: “How likely are you to change your design once you start manufacturing?”

The reason this question is necessary is the “cost of changing the design,” and this cost depends a lot on the process you choose. For example, for 3D printing, a change may only require updating the CAD file and reprinting the affected parts. However, once tooling is involved, the same change may mean modifying a mold that has already been designed and made.

What Happens When the Design Changes?

An example published by Plastics Engineering magazine shows how quickly these costs can add up. In one injection molding project, engineering changes made after the mold was completed added an average of about $5,000 for each change. One project required three changes to both the moving and fixed halves of the mold. This not only added $30,000 to the mold cost, but also delayed the product launch by four weeks.

Table 3: What Does a Design Change Mean for Each Process?

How a design change affects cost, lead time, and engineering effort depending on the manufacturing process.

Here, we can also give a design standard to help you judge the design gate for these processes.

How Mature Does Your Design Need to Be?

Table 4: How Mature Does Your Design Need to Be?

The minimum level of design maturity required for 3D printing, vacuum casting, low-volume injection molding, and production injection molding.

After we have seriously considered the purpose of making this batch of parts and the current design maturity, the next thing we need to focus on is the “final production material.”

First, the material itself is part of the product. It represents properties such as strength, stiffness, heat resistance, impact resistance, chemical resistance, and even surface appearance. These are not things that the manufacturing process itself can replace.

For example, a part that can snap together when printed with PLA or ordinary resin does not mean that it will also work properly when the final part is injection molded with PA66-GF.

When the design is basically determined, we need to start considering mechanical, chemical, and electrical properties. Using production-grade materials can help us evaluate material selection and final performance more accurately.

Therefore, material selection is a very important dividing point here. Even if you have already determined the final material, it can in turn limit whether you can use a certain process to validate it.

We can say that material affects not only the performance of the part, but also the manufacturing process. This is because different manufacturing processes use materials in different physical states and have different processing mechanisms.

How Does Material Affect the Process?

Injection Molding Station at TCT 3Sixty
Image Source: ©3DWithUs – Photo by Max Funkner

Read more from Max: Can 3D Printing Replace Injection Molding?

• 3D Printing: Depends on the material processing method, such as FDM melt extrusion, SLA photopolymerization, and SLS powder sintering. It mainly affects layer bonding, shrinkage and warping, and surface quality.
• Vacuum Casting: Depends on the flow and curing of liquid resin in the silicone mold. Resin viscosity and curing properties mainly affect filling, demolding, and surface reproduction.
• Low-volume IM: Depends on the rheology and crystallization of thermoplastics. Melting and shrinkage behavior mainly affect mold design, molding parameters, and shrinkage.
• Production IM: Based on low-volume IM, it further requires the material to match long-term production conditions. It mainly affects the processing window, cycle time, yield, and batch stability.

How Well Does Each Process Match the Final Material?

More importantly, the “real representation” of the material in different processes is fundamentally different.

3D Printing: If you only need to validate dimensions and appearance, there is a lot of flexibility in material substitution. But if you need to test mechanical properties, material substitution can make the result less accurate.

Vacuum Casting (VC): This is a very special transition process. It can reproduce the appearance and feel of the final product relatively well, but casting resin (PU) is not the same as the final thermoplastic used for injection molding. It can reproduce the “geometry,” but it cannot fully reproduce the “final material behavior.”

Low-volume IM (L-V IM): This is a change point. From here, we use real thermoplastic material + real injection molding, so it is very suitable for functional testing.

Production IM: This is the final stage. Material does not only determine performance, but also determines “whether it can be produced stably with a specific mold and machine.” Shrinkage and melt flow can affect the design of the gate, runner, and cooling system.

So, when answering this question, how should we choose the specific process?

Table 5: What Material Requirements Does Your Process Need to Meet?

How different material requirements, from basic geometry validation to final-material testing, can lead to different process choices.

At this step, we will really start to consider manufacturing cost. It should be pointed out that among these processes, this is not simply part price × quantity, but the real commitment, risk, and total cost.

First, let us sort out the cost structure of these processes.

What Does Each Process Cost?

FDM 3D Printing with PEEK for Mechanical Parts

FDM 3D printed mechanical part made with PEEK, showing the layered surface typical of FDM printing.

Image source: IN3DTEC

3D Printing – part cost × quantity + finishing.
The advantage is that the upfront fixed investment is low, but the economic risk mainly comes from the fact that after repeated production of many parts, the total part cost can become very high. – Higher unit cost, lower commitment

Vacuum Casting for Glossy ABS-like Parts

Vacuum cast ABS-like part with a glossy surface finish, produced using a silicone mold.

Image source: IN3DTEC

Vacuum Casting – master + silicone mold + casting parts.
There is clearly more upfront commitment here. The difference between VC and 3D printing is that you are not buying 100 parts, but buying a mold system that can reproduce the design in small quantities. – Moderate upfront investment, moderate commitment

IN3DTEC Low-Volume Injection Molding Process

Image Source: IN3DTEC

L-V / Rapid IM – tooling cost + part cost × quantity.
Here, tooling commitment is added. We can use aluminum molds to lower the tooling investment. The economic logic can be understood as: you are willing to spend some money first in exchange for a lower unit cost later, as well as the ability to use real thermoplastic material. – Tooling investment in exchange for lower unit cost and production-grade thermoplastic parts

Injection Molding for Consumer Electronics Casing

Injection molded consumer electronics casing with a smooth surface, uniform walls, vents, and mounting features.

Image source: IN3DTEC

Production IM – tooling commitment + volume commitment + material commitment + manufacturing commitment + supply commitment.
At this stage, we are no longer focusing on whether the design is correct, but on risk management around production speed, people, scrap, daily yield, and so on. If our product decision is wrong at this stage, the loss may not only be one mold, but the whole production plan. – High upfront and long-term production commitment

How Much Commitment Can You Take On?

Based on this, our question should not simply be “How much budget do you have?” but “How much risk can you take during the manufacturing of this batch of parts?”

Here we also have a checklist that can help you make the decision.

Table 6: Manufacturing Commitment Checklist

Key cost, tooling, production, and risk factors to consider before committing to a manufacturing process.

Engineering Decision Tree: Choosing the Right Manufacturing Process

An engineering decision framework for selecting 3D printing, vacuum casting, low-volume injection molding, or production injection molding based on validation goals, design maturity, material requirements, and manufacturing commitment.

Image source: IN3DTEC Technical Team

Through this article and the final engineering decision tree, I believe you should now be able to judge more systematically which manufacturing process the next batch of parts should use.

I believe you will also notice that throughout the whole article, we did not mention quantity as an independent core decision factor for these three processes. The reason is that we believe simply considering quantity is far from enough to make an engineering decision.

Just like the typical situation we set at the beginning of the article, the quantity was already given to you from the beginning. But we still need to think about other key factors to decide which process we should choose.

Do you have a project that needs to be manufactured now, or are you still hesitating because you do not know how to make the decision? Contact us, and IN3DTEC will give you professional advice based on your current situation.

In addition, IN3DTEC provides 3D printing, VC, low-volume IM, and production IM services. Welcome to learn more.