Introduction: Why Aluminum Extrusion Machining Matters
Another highly practical approach to producing functional, relatively strong, low MW aluminum components is aluminum extrusion machining. In contrast to machining a functionally-ready complete component from a machined aluminum block, many manufacturers are preferring to form the aluminum component by first cast / formed as near-net-shape aluminum extrusion, then carried through all the machining processes including CNC machining, sawing, drilling, tapping, milling, slatting, deburring and finishing.
This method is frequently applied for the manufacturing of industrial automatic systems, transport, electronic, energy appliances, cases, frames, heat dissipators, construction, medical and construction systems. The explanation is very simple, the extruded item give us the general shape of the system and the machining process get the tolerances that the extrusion cannot provide.
Per your engineering, buyers, and sourcing teams evaluating manufacturing routes, Professional Aluminum Extrusion Machining Services can serve as an important ‘benchmark’ against which to compare the combination of extrusion, CNC machining and finishing within a single process.
What Is Aluminum Extrusion Machining?
Aluminum extrusion machining relates to the second machining operation of aluminum extruded profiles. In extrusion process, the heated aluminum billet is forced through a die of the required cross section shape until a long aluminum extrusion profile is obtained. The extrusion profile is then cut to the desired length and machined into a finished or semi-finished article.
Standard machining practices include precision sawing, CNC milling, boring, drilling, tapping, countersinking, reaming, pocketing, slotting, end machining, face machining, deburring, etc. In some applications the part is anodized, powder coated, brushed, polished, chromate conversion coated, etc.
Value of the process derives from melding of these two assets. The extrusion provides the ability to generate long, very light weight and intricate cross-sections with internal cavities, ribs, fins, bosses, screw channels and mounting features. Machining additive accurate holes, flats datum surfaces, threaded pockets, connector interfaces and tight tolerance assembly features.
This combination can be used by manufacturers to reduce amount of machining needed while still maintaining the desired functional accuracy. In essence, extrusion produces the ‘roughing’ and machining produces the ‘finishing’.
Why Not Just Machine From Plate or Billet?
Machining from billet can be useful for prototypes, low volume or parts with complex 3D geometry, though if the part is to be repeatedly produced this results in excess material and machining time. Where the shape of the part has a constant cross-section, the procedure for machining from aluminum extrusion tends to be more useful.
Common examples are a machined rail, enclosure body, linear actuator housing, LED heat sink, battery tray member or structural framing member, which frequently all have a constant profile lengthwise. An initial extrusion of that section reduces potential CNC non-cutting time further with increased reduction in cycle time, chip volume, tool wear and raw material usage.
The economics get especially compelling when the profile integrates all the aforementioned features. One extrusion may contain mounting grooves, cable channels, cooling fins, screw bosses, alignment ribs, and aesthetic surfaces. Machining then occurs around holes, slots, faces, threads, and cutouts.
The part may become a substitute for many fabricated parts.
Why Machining Is Still Necessary After Extrusion
Extrusion is more efficient, but not equal to, precision machining. Surface tolerances in extruded aluminum sections are dependent on die specifications, alloy, wall thickness, complexity of the section, cooling, stretching, straightening and aging. For a large number of industrial components, extruded tolerances are sufficient for the general shape but not for bearing seats, connector locations, tapped holes, sealing surfaces, accurately-machined slots or close-fit assemblies.
That’s why a better design is one that segregates “excursioncontrolled” features (holes, thin walls, fins &guides) from “machining-controlled” features (interfaces).Non-critical features can “stay as-extruded” and the critical interfaces can be machined from robust datumes.
It could be the case that there is no need for tight tolerance on all outside walls such as the basic structure of a component made from aluminum profile. However, where the part incorporates threaded mounting holes for a motor, flat sealing face or dowel-pin locations, then these areas of the part should be CNC machined and measured to ensure compliance.
Common Aluminum Alloys Used for Extrusion Machining
The most widely used alloys in aluminum extrusion is the 6xxx series. Out of all the 6xxx series alloys 6061 and 6063 are the most frequently used—since they provide the optimum mixture of extrudability, strength, corrosion resistance, machinability, weldability, and finishing response.
6061 is chosen where higher strength is required. Widely used for machine building components, structural and architectural profiles, transportation components and parts, fixtures, brackets, frames and engineering.
6063 is generally used where good surface quality, good anodising response, good corrosion resistance and good extrudability are necessary, since it is used very extensively in the manufacture of visible profiles and components such as electronic enclosures, frames and components, where surface quality is as important as mechanical properties.
Other alloys might be chosen for special needs. 6082 can sometimes be found in more heavy-duty structural applications. 6005 and 6005A are found in transportation and structural extrusions. 7075, while having a high strength, is not as versitile as many 6xxx series alloys in terms of ease of extrusion processing, nor as corrosion resistant; so is normally only used in applications where their strength to justify its cost.
Best alloy can be chosen for strength, machinability, corrosion resistance, surface finish, anodizing, heat flow and production quantity.
Machinability: What Makes Aluminum Extrusions Different?
Aluminum alloys tend to machinemore readilythan steels. However, that does not mean that all aluminum extrusions machinemanageably. Depending on the alloy chemistry and temper, grain structure, heat treatment, wall thickness, profile stability, and residual stress, different extrusions will have varying machining characteristics.
In the case of extrusion machining, the difficulty is not just the cutting speed. It is the stability of the part. Thin walls can vibrate.
Hollow sections can distort under clamp pressure. Long profiles can bow or warp. Intermittent cuts can generate chatter.
Deep pockets can inhibit chip flow. Poorly planned fixturing can induce a variation in dimensions from batch to batch.
A good machining practice employs sharp tools, rigid workholding, cut chip flow, proper coolant use and realistic tolerances. For high-volume machining, special fixtures are at least as important as the CNC machine!
Another important aspect of the fixture is that it provides support for the extrusions. It can prevent them crushing, aids the positioning of the datum point, and damp loads which would otherwise cause vibration from the machining process as well as ensures the loading can be repeated. This is particularly critical for uses with long aluminum profiles, thin wall parts, and non structural hollow sections, or ornamantal components where clamp marks should not appear.
Design Rules for Better Aluminum Extrusion Machining
The ideal aluminum extruded machined part is conceived as an extruded-and-machined part—initially not a billet machined part subsequently converted to extrusion.
Use added material sparingly. Consider that any feature can be extruded into the cross section. Ribs, hollow chambers, bosses and fins can all be formed without drilling or machining.
This saves weight and time.
Second, steer clear of excessive thick-to-thin wall transitions. Large differences in wall thickness can make extrusion more difficult and can lead to uneven cooling or dimensional instability.
Third, know the function datums. The designer needs to state which surfaces control assembly, sealing, moving or aligning. Only those surfaces are machined.
Non critical ones should not have impossible specifications.
Fourth, do not go too deep and narrow unless it is genuine necessity. Deep pockets will increase tool deflection and cycle time, and will be more likely to produce burrs and cause chip evacuation issues.
Fifth, where possible, use nomenclature for standard hole sizes, threading sizes, and cutter-access geometry. A part that can be produced with standard, commercially available end mills, drills, and taps will be much easier to quote, quicker to produce, and easier to verify.
Sixth, schedule for finishing Anodizing, powder coating, and conversion coatings can alter surface appearance and occasionally affect the dimensional interface. Define threads, electrical contact areas, grounds, bearing fits, and masking needs prior to production.
Tolerance Strategy: Where Buyers Often Make Mistakes
Using tight tolerances on the whole extrusion. This can and often does increase cost but have no impact on the function. Thinking that a profile will behave like a machined block.
The profile can move if it is long and thin, or hollow for example, during cutting, after unclamping or after finishing.
A practical tolerance strategy has three levels.
What are the levels of process variation in injection molding?
In the first level is the normal extrusion tolerance, where general profile geometry, non-critical outside surfaces as well as non-assembly limiting features.
2. Precision extrusion tolerance may be necessary on any moderately critical dimensions, if the extruder can demonstrate delivery is still achievable.
The third is machined tolerance: Reserved for holes, slots, faces, threads, sealing surfaces, bearing features and datum-controlled interfaces.
It is important as it may be that the lowest cost solution is not the loosest tolerance. The optimal solution is one in which the tolerance scheme reflects the actual function of the part. If the accuracy is required only in certain areas for assembly, then these areas should be machined and checked, and the remaining profile to be extruded to the normal tolerance.
CNC Machining Processes for Aluminum Extrusions
The usual first step is precision cutting. Extruded profiles are cut to length using circular saws, automatic saw lines or CNC saw systems. Cut quality is important because the cut face could become a datum or may be machined in the future.
Milling—used to generate flat planar areas, slots, pockets, side windows, end features and mounting interfaces. Drilling and Tapping—used to generate screws, fasteners, connector plates, hinges, brackets, sensors, covers. Countersinking and Counterboring are commonly used for flush fasteners.
Reaming- may be used for dowel pins or accurate location holes.
Long length extrusion machining may even require special equipment. Many different large aluminum profiles require long bed CNC machines, multi-axis machining or special fixturing to prevent repositioning errors. Such a capability would be especially useful in rail systems, large frames, transportation profiles, architectural components, and machine building.
For more complicated components, 4- or 5- axis CNC machining can reduce fixturing and position errors. The machine can access more than one surface within a single set-up instead of repeatedly fixturing the component.
Surface Finish and Appearance
The surface finish is also one of the reason, Manufacturers prefer to use the machining process in aluminum extrusions. An extrusion of an external shape can be good enough, but to obtain precision features, machining process is used. But machined and extrusion surface effects are not always similar after anodizing or coating.
Visible areas. It must be specified if machined areas are suitable as visual surfaces. Anodising can produce tool marks, cutter path lines, deburring ‘bloom’, and directional flow marks.
If appearance is vitally important then the drawing should specify surface finish requirement, direction of brushing, class of anodising, any color tolerances, masking requirements and acceptable cosmetic limits.
6063 is mostly specified for visible anodized profiles due to its surface and finishing response. 6061 may give better strength but can produce different cosmetic results for different surface treatment/machining condition.
For industrial parts, surface finish is more than appearance. It may influence corrosion resistant, wear, electrical contact, thermal contact, sealing and ease of cleaning. For example, a heat sink may need a machined flat thermal interface.
An enclosure may need anodised or powder coated surface protection. A contact area might need to have coating stripped off, or Masked.
Cost Drivers in Aluminum Extrusion Machining
The cost of aluminum extrusion Machining is from the Extrusion-side and Machining side.
Extrusion-side cost is alloy related, depends on the size of the billet, complexity of the profile, the die design, the profile wall thickness and hollow or solid profile, tolerance needed, minimum order quantity, surface finish, and subsequent heat treatment.
Cost of machining is a function of the number of setups, fixture costs, part length, tolerance, holes, threads, burr containment, tool access, inspection methodology, and finishing. Five setups with hand deburring, close tolerances, and cosmetic anodizing will be substantially more expensive than a simple saw cut, drilled profile.
Design should be cost effective. For example, the number of set-ups should be kept low. If the holes are accessible from one or two sides, the machining is quicker and more repeatable.
Providing screw bosses or locating grooves in the profile means less material removal in the CNC machine. Only allowing the tolerance where absolutely necessary reduces inspection and reduces scrap.
Most of the cost savings were found in optimizing the design early on. After an extrusion die and some production fixtures have been manufactured, changing the design becomes more costly. This is why the engineering review before tooling is very important.
Quality Control for Machined Aluminum Extrusions
Insuring quality before machining is a reliable aspect of quality control. Supplier must insure the alloy, the temper, the extrusion tolerance, the straightness, the twist, the surface condition and traceability of batches. Material certificates and first-article inspection reports are probably used for critical parts.
Key controls during machining are fixture repeatability, tools monitoring, coolant conditions, chips evacuation, burr inspection and dimension inspection during the process. Final inspection will be done through CMM, height gauge measurement, thread gauges, pin gauges, surface roughness measurement, coating thickness measurement or visual appearance.
The best quality plans link inspection to function. A hole pattern that makes an electric motor, sensor, hinge, or linear guide ought to be checked more than a non-critical clearance slot. A sealing surface should have more surface and flatness control than hidden internal rib.
Quality control should also include finishing. Anodising or coating after machining may leave scratches, burrs, tool marks or handling damage. If the part is cosmetic, the supplier should specify inspection lighting, viewing distance, acceptable defect levels and packaging requirements.
Applications of Aluminum Extrusion Machining
The most common application of aluminum extrusion machining is in industrial automation frames. These machining can also be found within the frames of robotic equipment, all types of linear motion equipment, conveyor structures, machine guards, sensor brackets, pneumatic actuator housings, control cabinet frames, and modular workstations.
Common uses in electronics and energy include: heat sinks, inverter enclosures, LED lighting housings, power supply enclosures, EV battery trays, solar mounting rails and thermal management components. It is especially advantageous for heat sink applications since fins are readily generated as part of the profile, machining capabilities add mounting holes and flat thermal contact surfaces as well as connector cutouts.
Transportation applications: Rail systems, truck bodies, electric car formations, interior applications in aircraft, marine parts, support members lightweight,etc. Aluminum’s low density combined with high strength-to-weight ratio makes attractive in the light weight structures.
Medical and laboratory equipment. Aluminum extrusion machining is used for instrument frames and housings, as guide rails and brackets, protective covers, and modular systems. These tend to be fairly clean for surface finishing, dimensional repeatability.
How to Choose an Aluminum Extrusion Machining Supplier
A good supplier should know about extrusion and machining. Some machine shops are capable of machining accurately, but do not understand the behavior of the profile after extrusion. Some extruders have high output of profiles, but the machining potential is less sophisticated.
For more complex parts, the best solution might be one supplier, capable of screen the profile in consultation with the designer, give a advise on alloy and tolerance limits, construct the fixtures, machine the part, perform inspection procedures and supply finishing services.
Buyers may wish to ask some plausible questions: Can the supplier back-analyse the extrusion drawing prior to die manufacturing?
Can the supplier identify those parts of a feature that should be made by extrusion, and those that should be machined?
Is the supplier experienced with the alloy and temper?
Can the supplier machine long profiles with less machining repositioning errors?
Can the supplier anodise or coat without damaging machined features?
Is the supplier able to offer first-article inspection and batch traceability?
If the project is complex the communication is every bit as important as the capacity of the machines. The supplier should be able to inform about the possible design risks, make changes that will reduce the costs, justify how the part will be held, machined, finished, inspected and packaged.
Conclusion: The Best Results Come From Designing for the Process
“Aluminum extrusion machining” is not just the fabrication of “CNC machining aluminum” for it’s own sake. It is a manufacturing approach, exploiting extrusion for its ability to make highly efficient geometries, and machining for its ability to make precise function. Done properly, it minimizes material wastage, maximizes machining efficiency, enhances repeatability, and allows light-weight parts with built-in features
The secret is to bring the extrusion and machining experts in as early as possible. Choose the correct alloy. Extrude for shape.
Machine for critical interfaces. Tight tolerances at apm. Design for fixturing, finishing, inspection, and assembly from the start.
For aluminum producers that require light-weight, accurate, repetitively, and low-cost aluminum parts, aluminum extrusion machining remains one of the most useful manufacturing technique existed.
