OEM CNC machining services

The right supplier can provide machining services that can make essentially any part from any engineering material. You may be looking for a one-off to evaluate your design, some samples for field validation purposes or mass production of high value, high strength, high precision components.

A capable OEM CNC machining service provider will be able to help steer you in component design, materials selection, part splitting/combining for cost reduction and more.

OEM CNC machining is considered ‘extractive’, that is to say the net shape of the required part is extracted, by cutting, from a billet of high grade material that has the required properties – this results in the net shape of the part AND high value scrap material that is generally well suited to recycling.

What is a CNC machine?

Machine tools operated by OEM CNC machining services differ from manually operated machines mainly in that they operate under Computer Numerical Control (CNC). A CNC machining centre is a mill, lathe, drill or Electrical Discharge Machine (EDM) that integrates computer control, automatic tool changer and often automated means of loading and unloading workpieces. This group of machines have become more diverse and complex and are able to undertake highly automated machining tasks.

Various machines are used to achieve the wide range of functions in complex component cutting;

A CNC lathe rotates the material to be worked, and applies various cutting tools to remove material according to a tightly controlled and highly repeatable fashion. A lathe is the ONLY machine that can make parts more accurate than itself and these were the first machine tools to be automated – long before digital controls existed.

CNC mills come in a wide variety of formats. They (generally) hold the part to be machined in a vise which can be moved on three axes (x-y-z) and presented to a rotating cutter spun on a vertical or horizontal axis. However, the range and diversity of machines has lead to this class being referred to as Machining Centres, as axes, capabilities and tools have increased in range. Many OEMs now offer 3, 4, 5, multi axis (‘composite machine’) and multi-axis (‘gantry’ type) machining services – as the tooling axis or axes can move between angles (horizontal to vertical), as clamping/vices can rotate to present alternate part faces, as cutters become smarter (including in-cutter sensors) and as the machine can essentially switch between lathe and mill functionality.

EDM (Electrical Discharge Machining) systems exist in two basic forms – wire cut and ‘conventional’  or die-cut erosion machines. Wire-cut systems came first, despite the ‘conventional’ label. Both types use pulsed discharge of an electrical current between the tool and the workpiece immersed in dielectric fluid to slowly erode material. Tool position is usually withdrawn on the cut axis, between discharge pulses, to allow cut materials to be watched out of the workplace. Wirecut feeds the sacrificial wire progressively as it erodes the point-cut as the part is traversed in 3 axes to create the cutter path. Conventional erosion machines use precision tools as the eroder, faithfully reproducing a negative of the tool in the workpiece. Both approaches suffer from tool erosion affecting precision, so die-cut tool materials are selected for relatively low erosion – very pure Carbon and Copper are used for this property – and wire-cut electrodes are fed to compensate for it.

Types of machine used by OEM CNC machining services

Machines can be used to make required components of a product, or they can be used to machine components for high volume manufacturing tools for higher capacity processes, which in turn then make die-cast, moulded, stamped, coined, pressed or forged parts parts. A wide variety of specialist cutting tools can perform various specialist operations such as tapping and drilling to create the required part. Machining centres, lathes and EDM machine tools are capable of producing parts within very tight tolerances, which refers to the accepted limits of deviation from the specified dimensions.

OEM CNC machining suppliers programming and machine setup can take a considerable amount of time and requires imaginative, experienced and up to date skills from the operations staff. However, once the machining processes and loading/unloading of workpieces is set up, little further operator intervention is required. On this basis, these machining methods make very expensive one-off parts and are often used in the mass-production of components. For example, Apple and many high-end phone manufacturers use

Machine types and programming complexity are generally defines by the number of motion coordinates of the machining centre and the number of coordinates controlled at the same time: there are three axes and two linkages, three axes and three linkages, four axes and three linkages, five axes and four linkages, and six axes and five linkages. Three and four-axis refers to the number of motion coordinates of the machine, and the ‘linkage’ describes the number of coordinates that the control system can simultaneously control the motion of, thereby increasing the flexibility of the position and speed control of the cutting tool, relative to the workpiece.

Process accuracy, repeatability and tolerances

OEM CNC machining suppliers processing accuracy is a major differentiator of machining services. Service providers use general machining tolerances for the most widely fabricated parts, working to higher precision and repeatability where it is required. Standard machining tolerances for aspects such as threads, pins, pipes etc are widely accepted and understood. OEM machining services offer typical general tolerances of +/-0.1mm, applied where the part drawings don’t specify tolerance levels. Much closer control is possible – but it requires the sharpest tools and slower feed rates, making it more costly to achieve both in consumables and machine time. On that basis, tolerances should be relaxed where possible and specified tightly only where critical.

Tolerances required by OEM CNC machining suppliers are provided in three formats, which denote greater or lesser requirements;

Bilateral or Unilateral tolerances specify a range within which a dimension must be held – bilateral allowing plus or minus limits on the feature size (10mm +/-0.1mm), unilateral specifying a single upwards or downwards limit (10mm +0, -0.1mm).

Limit tolerancing is similar to bilateral or unilateral – except the final accepted maximum and minimum dimensions are specified (rather than a target and limits). This lends itself to inspection and to go-no-go gauge use.

Geometrical tolerancing which specifies tighter control of a wide range of features – flatness, parallelism, concentricity and more. This is a more universal system and common in high precision multi part assemblies where interactions between parts are key to function.

The range of standard machining tolerances is usually set by various international standards bodies such as the International Organization for Standardization (ISO), the American Society of Mechanical Engineers (ASME), and the American National Standards Institute (ANSI).

Advantages and disadvantages of OEM CNC machining

Advantages

A large number of steps in machining can be made, and extremely complex resultant net shapes can result from the use of less complex tooling. To change the shape and size of the part or add/remove features, the designer and programmer need only revise the cutter paths and tool types utilised in the processing program. This lends itself to one-off and part adjustments to enable evaluation of features.

OEM CNC machining suppliers process quality is highly stable, the resultant precision is high (if cutter maintenance is closely monitored), the repeatability of precision is high and the process lends itself to high precision/high strength component requirements, where cost is not the primary driving factor and volumes are low to moderate.

High production efficiency can be achieved in multi-variety and small-volume production, reducing production preparation time, machine tool adjustment and process inspection time, and reducing cutting time due to optimised cutter paths and cut depths.

OEM CNC machining processes can deliver extremely complex components that are difficult to manufacture by other methods and the methods can even deliver otherwise unprocessable parts. This gives design freedoms that can offer significant functional and cost advantages by reducing art count and post processing and reducing internal feature weaknesses and compromises.

EDM offers one significant advantage over more conventional machining processes. The ability to fine-process pre-hardened materials results in the highest net accuracy. Where parts are EDM spark eroded, the part material can be directly used in high wear and high stress aplications without the need for post machining heat treatment – which would otherwise result in heat distortion and either a loss of precision in the part or a need for complex post processing. It is for this reason that die-cast and mould tool cavity cutting is generally performed (or finished) using EDM in pre-hardened materials.

Disadvantages

OEM CNC machining suppliers machine tools are expensive and require high grade space and services, making their hourly rate high.

While in operation, OEM CNC machining requires low labour – but setup, programming and maintenance all require experienced and highly trained staff, adding significantly to the overhead component of the hourly rate for services.

Processing times/throughput are relatively low compared with true mass production processes – the ‘single point of action’ at the cutter means every step is one piece production. Processing times for EDM are particularly long, making it highly inappropriate for mass production processing.

Material costs are high, compared with true mass production processes. For example, Apple Mac chassis machining from billet requires several hundred times the ‘input’ material than the ‘output’ component, compared with, for example die-casting, where this ratio is much more favourable.

Typical service options

Most OEM CNC machining services will work with the following materials:

Metals; Stainless steels and inconel, Brass, Super Alloys and Special Metals, Hastelloy, High Carbon steels and speciality alloy steels, Pre-hardened steels, Tungsten, Titanium, Aluminium and Magnesium alloys, Copper

Plastics/polymers; any free machining polymers, cryo processing of rubbers, PTFE and fluorinated co-polymers, Carbon and glass composites

OEM parts machining supports diverse industries;

Tools and die parts, Medical devices, Complex mechanical parts, Tubes and hollow components, Architectural applications, Consumer products, Aerospace parts, Instrumentation

File types and formats are very flexible (2D and 3D as data is not used directly, but interpreted in programming);

AutoCAD (DXF, DWG), Pro-E or Pro Engineer (DRW, PRT, and XPR), SolidWorks (SLDPRT, SLDDRT, and SLDDRW), Graphics Interchange Format (GIF), Portable Document Format (PDF), Parasolid (XT, XB), IGES (IGS), STEP (STP), Rhino, Solid Edge, Autodesk Inventor and more

Conclusion

Whatever your requirements, OEM CNC machining supplied parts can fulfil a very wide range of roles, from test/prototype to mass production , from high cosmetic to high stress applications and the process allows design freedoms that can unleash capabilities and reduce part counts in ways that more mass-production capable services cannot.

Quality and repeatability are key, and as with any industrial process these result from careful and highly capable interpretation of the design information in executing on parts.