3D Printing vs Injection Moulding vs CNC Machining

Introduction

Selecting the right manufacturing process for plastic components can be challenging. In this guide we compare three of the most common options 3D Printing (additive), CNC Machining (subtractive) and Injection Moulding (formative), to help you decide which is most efficient for your project.

These processes offer both opportunities and restrictions in realising your design. Considering the manufacturing process during the design stage, helps to leverage the strengths and mitigate the limitations of each process and can help you to understand which process is most efficient and cost-effective for your application..

Here we will compare industrial powder bed fusion (PBF) 3D printing processes to other plastic manufacturing methods in a side by side analysis of contract services for each method.

How to compare manufacturing processes

The following factors should be taken into consideration when choosing a manufacturing process.

1. Volume / Budget: How many parts do you need? Each manufacturing process has a relationship between quantity and cost. The number of pieces you need to make can determine which method is economically superior.
2. Lead time: When do you need your parts? Each process requires time for design verification; machine set up, manufacture and post-processes. How long you’ve got can determine which method is most suitable.
3. Materials / Finishes: What material properties do you need? Polymers are a versatile material group with thousands of material options; however, not all are available for each manufacturing process.
4. Design constraints: What is the geometry of your design? “Design for manufacture requirements” are the constraints that dictate which forms are possible to produce. Each process has different design constraints.
5. Process flexibility: Is your design _final or final_final? Making alterations to your design after the manufacturing process has begun can be problematic depending on the process.

Technology introductions

3D Printing (Additive Manufacturing)
	3D printing is an additive manufacturing process that creates parts by fusing layers of material together. There are multiple 3D printing technologies, but this article focuses on are: Selective Laser Sintering (SLS) and Multi Jet Fusion (MJF), both of which are polymer powder bed fusion (PBF) processes.
CNC machining
	CNC machining is a subtractive manufacturing process that removes material from a solid block to create parts. Similar to 3D printing, there are many types of CNC machining. In this article, we focus on CNC milling and CNC lathing.
Injection moulding
	Injection moulding is a formative manufacturing process that creates parts by injecting molten plastic into a cavity mould (tool). The types of injection moulding we focus on in this article are rapid & production tooling for single, multi-cavity and family moulds.

Technology Comparison Overview

The main decision-making factors for product manufacturing are shown in this table with comparisons between the three manufacturing techniques.

	3D Printing	CNC Machining	Injection Moulding
Start-up Cost	Lowest No cost	Small setup fee £100+	Tooling cost £3,000+
Volume*	Low to medium 1 – 10,000	Low to medium 1 – 5,000	High volume 10,000+
Lead Time**	Fastest 2 – 7 days	Medium 7 – 14 days	15 – 60 days
Material Selection	5+ plastics	20+ plastics, woods, metals	Broadest 100+ plastics
Surface Finishes	As-printed shows layer lines. Post-printing surface finishing methods are available.	As-machined shows tool marks. Post-machining surface finishing methods are available.	Broadest Numerous finishes including glossy, textured & matte.
Design Constraints	Few Freedom to design complex geometries	More limitations and complex geometries add cost	Many limitations, requires expert design for manufacture
Flexible Process***	Yes	Yes	No

* Number of units viable for a typical production run

** Lead times based on express service production
***Does this manufacturing process enable easy and consequence free design changes?

Section 1. Volume / Budget

Every project balances start-up investment against cost per part. Here’s how each process stacks up.

The total cost of manufacturing usually comes down to two things:

• Start-up cost – the fee to begin the process.
• Unit cost – the price per part produced.

3D Printing

3D Printing has no start-up cost, there’s no tooling, and no need for programming tool paths.
There is, however, a low minimum order cost (£30–£60) to cover setup, processing, and logistics.

The main driver of price is printing time. Each additive technology has its own pricing model, and material costs play a role too, but material usage isn’t always equal to the physical volume of the part.

For more details, check our pricing page, or upload a file to get an instant quote.

CNC Machining

CNC machining requires a small start-up cost, known as non-recurring engineering (NRE), to cover machine setup, part fixturing, and tool path generation.

The biggest cost factor is machining time (or cycle time). The longer it takes, the more expensive each part becomes. Material type matters too: hardened metals increase machining time and therefore cost.

Complex geometries raise the price further, as parts may need repositioning or multiple setups. Some shapes simply aren’t feasible with CNC.

Injection Moulding

Injection moulding has a high start-up cost, with tooling typically starting at £3,000 and rising sharply with part complexity, materials, and finish choices.

Once the tool exists, though, the process delivers an exceptionally low unit cost, with raw material being the main expense. This is why injection moulding only becomes cost-effective at high volumes, the savings per part must outweigh the initial investment. In fact, some tools can cost six figures but pay off across very large production runs.

Tool replacements are eventually required. Steel tools offer the longest lifespan (and highest upfront cost), while aluminium tools are cheaper but wear out sooner.

Quick Comparison

	3D Printing	CNC Machining	Injection Moulding
Start-up Cost	None (£30–£60 min order)	Small NRE fee (£100+)	High tooling (£3,000+)
Main Cost Driver	Printing time	Machining time (cycle time)	Tool amortisation + material
Best for	Low–medium runs and complex parts	Low–medium runs and precise tolerances	High volume production

While the table above gives a quick overview of how start-up and unit costs compare across processes, it doesn’t tell the whole story.
The real question is: how do these costs play out when you actually make parts at different volumes?

To illustrate, let’s look at a sample component and compare the total costs for 3D printing, CNC machining, and injection moulding across different order sizes.

Cost by Volume for an Example Part

Our sample item (above) is an electronic enclosure (75.0 × 38.0 × 58.0 mm). As shown below, the part is ideal for 3D-printed production, enabled by 3D nesting.
Process	Material	Quantity	Tooling Cost	Unit Cost	Total*
Injection Moulding	Nylon	1	£5,429.27	N/A	N/A
		500		£0.92	£5,889
		5,000		£0.38	£7,329
CNC Machining	Nylon	1	N/A	£125.20	£125.20
		500		£8.06	£4,030
		5,000		RFQ	RFQ
SLS 3D Printing	Nylon	1	N/A	£15.59	£15.59
		500		£2.64	£1,320
		5,000		£2.35	£11,750

* Totals shown are indicative and for comparison only. Nesting efficiency, packing density, geometry, material and finishing will affect final pricing.

The table above shows how costs stack up for one specific enclosure, but the same principles apply across most projects. To put it in context, the graph below highlights the broader trend: how unit cost falls as volume increases, and how the three main manufacturing technologies compare with each other.

You can clearly see where 3D printing is most competitive at low to medium volumes, where CNC holds its ground, and where injection moulding eventually pulls ahead once tooling costs are spread across thousands of parts.

Multiple part assemblies

Does your product need to be made from multiple components? This question is essential to consider because it will influence your decision-making process. If your product consists of many parts and you are looking to produce it with injection moulding, you are going to need numerous moulds or a family tool. The additional tooling requires an increased start-up cost. By comparison, 3D printing and CNC machining have no tooling costs, so it’s more affordable to produce more parts.

Section 2. Manufacturing lead times

Speed to market can make or break a product launch. Lead times vary widely depending on process.

Lead time: When do you need your parts? Each process requires time for design-verification, machine set up, manufacture and post-process. How long you’ve got can determine which method is most suitable. In general, these are the lead times for the three manufacturing processes:

• 3D Printing – 2-7 business days
• CNC Machining – 10-25 business days
• Injection Moulding – 20-60 business days

Different companies often have different lead times, so you always want to confirm before developing any specific expectations about when you are going to get your first product. Factors outside of your control, such as their current workload, operational capacities, and staffing, will affect the lead time you are going to get.

3D printing is the fastest way to begin producing products, enabling you to get your first item in a matter of days.

Section 3. Materials & finishes

For functional parts that require strength and durability material selection will be of utmost importance. Post processing and finishing are also essential for the usability and appeal of your product. There are a range of post processing techniques that can be used to finish a product, but these can add time and costs to the overall unit cost. It is also possible to create a finish by including textures in the design of the part.

3D printing offers access to a medium but versatile range of plastic materials and finishes, including but not limited to thermoplastics. The surface finish of polymer PBF 3D printed parts can be ‘relatively’ rough. A variety of finishes are available to smooth the surfaces, such as Vibro-Polishing and/or Vapour Smoothing. Full colour-match dyeing can also be applied to 3D printed parts. 

CNC Machining supports a decent number of plastic, wood and metal materials. With CNC you can get your product with an “as machined” or smoothed finish, together with any designed patterns.

Injection Moulding can utilise many thousands of different materials, including thermoplastics and silicone rubbers. IM parts can come with a variety of finishing options such as bead blasting, etching, and matte finishes. Also, dual shot injection moulds create products with two materials in the same cycle, such as plastic toothbrushes with a silicone grip.

Section 4. Design constraints

Not every design is suitable for every process. Each comes with its own rules.

How complex is your part geometry? Design-for-manufacture requirements are the constraints that dictate which forms are possible to produce with a given process. Each process has widely different design constraints.

These constraints include minimum thickness, draft angles, undercuts and many more. See our design rules for 3D printing to help design for our service.

Section 5. Manufacturing process flexibility

As designers, we understand that a product can always be improved. The question is how expensive that change will be.

Even though it’s likely that you’ve designed, prototyped and iterated, sometimes specific features of the product get overlooked. Occasionally, changes need to be made during the manufacturing process.

3D printing is the most flexible technology between the three. It’s incredibly easy (and comparatively much cheaper) to stop production of one design, edit and update the production run. If you are still developing, most often than not you print multiple iterations simultaneously, especially when using MJF or SLS 3D printing.

CNC machining is similarly flexible in its ability to absorb design changes without significant financial consequences. However, changes need more time and require some additional cost.

Making changes with Injection Moulding is extremely difficult in comparison to the other two manufacturing methods. To facilitate a significant design alteration, you may need to remake the tooling from scratch. There is a small window of time during the mould making process where you can run some test units and make minor changes to the tool before it gets hardened.

Once you are happy with your design, the mould gets hardened, and further changes become incredibly slow and expensive.

At 3D People, we often use MJF or SLS 3D printing to manufacture the initial release of a product. 3D printing alpha product runs enable our customers to take their product to market, test the waters, and improve their design before volume IM manufacture.

Conclusion

Choosing the right manufacturing process is crucial to your product’s success. There are various factors to consider, as we have outlined here. However, the “correct” technology will ultimately depend on your application and your priorities.

	Pros	Cons
3D Printing	• Creates complex geometries • No start-up tooling cost • Fast turnaround, instant ordering • High design flexibility • Broad colour options	• Expensive for large parts • Limited material & finishing options • Smaller discounts at high volumes
CNC Machining	• Low set-up cost (minimal NRE) • Excellent surface finishes • Wide range of metals and plastics	• Less cost-effective at scale • Higher unit cost than moulding • Complex shapes increase price
Injection Moulding	• Very low unit cost at scale • Strong, durable products • Wide material and finish choice • Dual-shot / overmoulding possible	• High tooling cost (£3,000+) • Long lead times for new tools • Visible parting lines & ejector marks

There’s no single “best” process; each has its strengths.

• 3D printing is ideal early on: low start-up cost, fast turnaround, and freedom to experiment.

• CNC machining offers precision and strength, though at a higher per-unit price.

• Injection moulding is the clear winner at scale, but only once you can justify the tooling cost.

The smartest approach is often hybrid: start with 3D printing to prove the concept, use CNC for critical functional prototypes, and move into injection moulding when demand is ready.