Small Batch Production in Metal / Plastic

More than a one-off, less than a series

Small batch production means manufacturing a component in a limited quantity. That is more parts than a one-off, but too few to justify a dedicated mould or production tool. Typical occasions are the pilot run after the prototype, spare parts for machines and systems, custom builds and product variants, components for fixtures and toolmaking, or products whose sales cannot yet be predicted. For metal parts, CNC machining is often the right process. It works directly from the drawing and the program, without part-specific tooling. The following sections show which components are suitable, where the limits lie and what you should prepare for an enquiry.

What small batch production is and how it differs

Small batch production is the manufacture of identical parts in small quantities. It sits between one-off production and high-volume production. There is no fixed threshold in units. Whether ten, fifty or a few hundred parts still count as a small batch depends on the component, the process and the industry. The main difference lies in how often a part is produced and how much preparation is needed.

One-off production

In one-off production, a part is made exactly once, for example a prototype or a spare part for an older machine. The program, workholding and inspection are set up for this single piece.

Small batch

In a small batch, the same part is produced several times. The program and the setup are created once and then used for every further part. This is why it makes sense to design the processes for repeatability from the start. For small batch sizes, the effort required for moulds, casting patterns or injection moulding tools is usually too high. What is needed is a process that works without this upfront investment.

High-volume production

High-volume production relies on processes that deliver very large numbers of identical parts in a short time, such as die casting, forming or injection moulding. These processes usually require a dedicated tool for each component, and producing that tool takes time. This is worthwhile mainly for high quantities.

Five reasons why CNC machining suits small batches

CNC machining is based on an NC program created from a drawing or CAD data. This results in five advantages for small quantities:

1. No forming tool is required. The part is machined from solid material, without a mould or casting pattern.
2. The path to the first part is short. As soon as the program and setup are in place, production can begin.
3. Changes remain possible. If a dimensional change is needed, the program is adjusted rather than a tool.
4. Results are repeatable. The machine processes every part using the same program. This is the basis for consistent dimensions across the entire batch.
5. Genuine production materials are used. The parts are made from the same metal that will be used later on. This matters when a small batch supplies functional parts rather than samples.

When a CNC small batch is not the best choice

CNC machining is not the right process for every small batch. If a component has internal channels or cavities that no tool can reach, they cannot be produced by machining. In such cases, 3D printing is often the better solution.

The same applies when a small batch turns into high-volume production. For very high quantities, processes such as die casting or injection moulding come into consideration.

Very thin-walled parts also need careful assessment, as they can deform during machining. Reviewing the drawing shows whether a part is feasible. An honest feasibility check before placing an order therefore makes sense. It clarifies early on whether the component is suited to machining.

Which components are suitable for CNC small batches

Components that can be machined from bars, blocks or plates are well suited. These include milled housings, brackets, plates and flanges, as well as turned shafts, bushings, pins and sleeves. Three questions help with the selection.

Can the geometry be achieved by machining?

External contours, pockets, bores and threads are typical features of CNC machining.

Which material is required?

Aluminium, stainless steel, brass, copper and engineering plastics are among the common materials used in machining.

How many sides need to be machined?

Parts with features on several sides benefit from 5-axis machining. A 5-axis machining centre can process a workpiece from several sides without having to reclamp it. Every new setup means additional setup time and is a potential source of dimensional deviations between the sides. If a part is machined in a single operation, these steps are eliminated. At the same time, complex contours and angled bores can be produced that would only be possible on a 3-axis machine with multiple setups or special fixtures.

Which machines are available

At Rinas, 5-axis machining is handled by a Hermle C250. Its working area is 600 × 550 × 450 mm (X, Y, Z). The table carries up to 1,100 kg. The spindle runs at up to 15,000 rpm, the magazine holds 30 tools, and positioning accuracy is ± 0.005 mm. A Gildemeister NEF 520 is available for turned parts. You can find out more about both machines on the CNC machining at Rinas page.

From prototype to small batch

Many small batches begin with a prototype. Two things are key to a successful transition to series production: the right process from the outset and complete documentation.

Producing the prototype using the series process

If the prototype is already CNC machined from the final material, the transition to series production usually goes smoothly. The program from the prototype phase forms the basis for the series. Findings from testing are incorporated into the program as changes. In this way, the first sample gradually becomes a production part without having to change the process.

What you should prepare for an enquiry

A complete enquiry speeds up the review and avoids follow-up questions. Helpful information usually includes the drawing or 3D data of the component, for example as a PDF and STEP file, the material with its exact designation, the quantity and, if foreseeable, the requirement for follow-up orders. Add to this tolerances and surface finishes, especially on fits and functional surfaces, details of the type and size of threads, and the requested delivery date. The clearer these points are, the faster a manufacturer can say how they will produce the part. You can send us your documents directly via the contact form.

CNC small batches with Rinas Gerätetechnik

At Rinas Gerätetechnik, we manufacture individual parts, prototypes and small batches at our site in Aftholderberg near Lake Constance. In addition to 5-axis milling and CNC turning, our services include drilling, sawing and thread cutting. We produce internal and external threads, including fine threads and special sizes. For quality assurance, we use our own measuring equipment and inspection devices. Our customers come from aerospace, medical technology, the automotive industry, toolmaking and mechanical engineering.

Are you planning a small batch and want to know whether your component is suitable? Send us your drawing for an initial assessment.