When Is It Worth Using 3D Printing?

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-06-05 00:21

Additive manufacturing is no longer just used for prototype production. According to a recent VDMA study, almost 50% of all machine builders now use 3D printing. Half of them use additive manufacturing for prototyping and the other half also for other applications such as series production, tools and spare parts. Many other machine builders are considering the application. The question of cost naturally plays a decisive role here: When is it worth using 3D printing?

What the use of additive manufacturing costs

The cost structure describes the ratio of costs to benefits and is therefore decisive for the question of whether series production makes economic sense or not. Since the cost structures differ from conventional and additive manufacturing processes, the cost factors must be carefully weighed up against each other. A first cost estimate for 3D printed products is usually made per cubic centimeter manufactured. Post-processing of additive components is also a cost factor.

When using 3D printing, the costs are largely determined by the acquisition costs of the 3D printer, followed by the costs for the materials and labor costs. However, other factors such as consumables (e.g. gas) and energy costs can be neglected. Machines for the production methods selective laser sintering (SLS) and laser melting (SLM) are very capital intensive. The cost of powder bed-based processes is often compared with that of tool-intensive conventional manufacturing processes such as injection molding and die casting, or with machining processes such as CNC milling (Figure 1).

Seminar tip

The 3D printing seminar in direct digital production conveys the technology, suitability and requirements of 3D printing and gives the participants an overview of the developments, possibilities and limits.

When is 3D printing worthwhile?

Despite the higher variable costs, the use of additive processes in production can make economic sense, as a look at the fixed costs makes clear. With classic manufacturing techniques, fixed costs are only distributed over a single, specific component design. For example, a mold in die casting can only be used to manufacture the specific product for which it was developed. Accordingly, the cost of the mold must be calculated based on the number of parts produced. The costs for setting up a machine tool or changing tools on an injection molding machine must be distributed across the number of parts produced in this production lot until the next changeover. If only a few units are produced per batch, the fixed costs can far exceed the variable costs,so that 3D printing is cheaper than manufacturing with conventional processes.

3D printing is also subject to a certain degree of fixed costs, but these can be more easily offset by different products that are manufactured in a single batch. The actual cost of an additive construction job per cubic centimeter depends on a complex combination of technical parameters and the operating conditions of the machines.

The most important parameters for powder bed-based processes:

• Machine data
• materials
• Construction job parameters
• Consumables data
• Operational calculations

One way to reduce the total cost of additive manufacturing is to change the parameters. Since laser sintering and laser melting machines are expensive to buy, the productivity of the machines is a critical parameter that influences the overall costs. The productivity of the machines results from the quotient of the actual throughput of a construction job (i.e. the exact material volume of the manufactured components) and the throughput time of the construction job (i.e. the time required to carry out the construction job).

It is therefore important to know the structure of the throughput time of the construction job in powder bed-based processes, since they are the key to optimizing the overall costs.

The lead time includes:

• Time to set up the machine, load the 3D files and remove the finished components
• Time that the machine needs for preheating and cooling in additive manufacturing
• Time that the laser needs to expose and melt all component surfaces
• Time that it takes to apply and, if necessary, warm up the powder layers
• If necessary, time for quality assurance in the ongoing construction job

Book tip

The contribution comes from the specialist book "Additive Manufacturing". The book by the team of authors at ETH Zurich describes the basics and practice-oriented methods for using additive manufacturing in industry and is aimed at designers and developers to support the successful implementation of additive processes in their companies.

The manufacturing time for the SLS process

If you look at the SLS process, the actual manufacturing time makes up about 90% to 95% of the total throughput time of the construction job. During this time, the printer is independent of the operator. The manufacturing time consists of preheating the machine, building the parts and cooling. The times for preheating and cooling are largely constant for each construction job and depend on the size of the installation space of the respective 3D printer. The actual construction phase takes around 60% to 70% of the production time, depending on the machine and the space utilization. The envelope volume, also known as the bounding box, is often used for an initial estimate of the space requirement of a component in the installation space.

In normal operation, the construction time itself consists of 50% exposure or melting and 50% heating or application of new powder layers. This information generally also applies to the SLM process, whereby the percentages differ in part significantly, since the melting of the metal powder takes place significantly more slowly.

A number of technical and operational measures can reduce the total cost per cubic centimeter. Technical measures on the part of the machine manufacturers are to reduce the time for exposing and applying powder layers, as well as the preheating and cooling times. This is often achieved by a larger number of lasers and the development of concepts for faster application of the layers. Figure 3 gives an impression of how significantly the production time can vary depending on the machine.

When it's worth having your own 3D printer

The company itself invests in additive manufacturing machines and operates them directly. In order for the machines to pay off, high capacity utilization is necessary. The following measures should also be taken into account in order to keep the total costs as low as possible:

• 1. Ensuring a tight filling of the installation space with components
• 2. Maximizing the share of actual exposure time in the total throughput time, for example through a high space utilization.

With laser melting, a tight packing can only take place on the horizontal plane of the machine, since the components cannot be manufactured in several layers on top of each other with this method. The laser sintering process achieves the best economy if the components are tightly packed in several layers one above the other. Figure 4 illustrates the impact of high build job packing density on the unit cost of a small lever. It can be seen how the total costs stabilize largely after the first layer is filled.

Accordingly, at least one dense level of components should be achieved for efficient operation of laser sintering machines. The discontinuities in the graph result from the fact that each time a new layer is started, the total time for applying the layers in the construction job increases. However, due to the shape of the components, the height of the components in the direction of assembly (z direction) usually does not use the entire available horizontal space (xy direction) of the machine. Accordingly, the increase in the time and cost of building up is not fully distributed to a new densely packed horizontal layer. It is therefore recommended that the height of the construction is planned as consistently as possible for the entire construction job. Individual areas that reach higher z coordinatescause the cost of the construction job to increase unnecessarily.

Job market

3D printing designers wanted like never before

In addition, the factors of time and component quality have to be weighed against each other in 3D printing, since higher quality always means an increased expenditure of time in production. The decisive factors here are the selected parameters, such as the layer thickness. Smaller layer thicknesses enable greater detail accuracy and better surface quality, but require more production time and thus increase the overall costs. Especially in laser sintering, the powder recycling factor also plays an important role in the construction costs. The higher the proportion of recycled waste powder, the cheaper the construction job. Too high a proportion of waste powder can influence the flowability and deteriorate the construction quality or even lead to defects in the manufactured components.

When it is worth sourcing 3D printed parts externally

As an alternative to in-house production, the user can also purchase 3D-printed parts from service providers. Initially, this is the easiest way for a company to gain access to additive manufacturing technologies. It does not require any specific knowledge about the operation of the machines and also no major investments in advance. The decision to purchase from a service provider also means lower risks and price fluctuations in production for the company, since the efficient use of the 3D printer is the responsibility of the supplier.

The prices for external purchases depend on the total material volume of the order as well as on the effect of the component shape on the space utilization. For example, large-scale lightweight structures can take up a lot of space on the building board, even though they have only a small volume of material. Orders with a larger volume of material and a higher packing density achieve lower price offers because they simplify the operation of the machines at the supplier.

What you should consider with 3D printing service providers

According to a study from 2014, two different pricing strategies can be identified for 3D printing service providers. The study compares 21 offers from different service providers worldwide and divides them into two categories:

Category A (purple ellipse):

The 3D printing service providers charge similar prices per cm³ for quantities of 1 and 100. Suppliers in Category A probably want to ensure that the space available for their machines is optimal by combining the orders of different customers. This allows service providers to offer stable prices per cubic centimeter.

Category B (green ellipse):

The 3D printing service providers charge higher prices for small quantities (between 5 and 10 euros per cm³) than for larger quantities (between 0.5 and 1 euros per cm³). These service providers obviously prioritize fast delivery and do not summarize or only subordinate orders. The resulting cost situation is more similar to that which would arise if the company manufactured its own equipment, i.e. inversely proportional to the quantity of the component volume ordered. If you know about these strategies of the service providers, you can better plan where it is profitable to shop.

More information on the specialist book

Seminar tip

The 3D printing seminar in direct digital production conveys the technology, suitability and requirements of 3D printing and gives the participants an overview of the developments, possibilities and limits.

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* * Dr.-Ing. Christoph Klahn, Head of pdz at ETH Zurich, Prof. Dr.-Ing. Mirko Meboldt, lead professor at ETH Zurich