What Is Aluminum Machining?- Tools, And Operations

What is Aluminum Machining?

Aluminum Machining is a subtractive manufacturing process that removes material from a workpiece to manufacture the desired part or product. It is a highly versatile process and can work with a variety of metals and non-metals substrates. One of the most common materials used in machining processes is aluminum.

Because of unsurpassed material weight, low material hardness, and higher formability, aluminum is the best for use in machining and other manufacturing processes.

Below, we will highlight some of the other benefits of using aluminum for machining applications, explain how aluminum is used in different types of machining processes, and identify some of the common examples of machined parts made of aluminum.

An Overview of Aluminum Machining Processes

“Machining” is a generic term that deals with multiple subtractive manufacturing processes e.g., milling, turning, drilling. In addition, there are many types of machining technologies and techniques e.g., CNC machining, swiss screw machining, vertical and horizontal milling, and electrical discharge machining (EDM). Here we explain how aluminum is processed in each of those machining methods.

• Computer numerical control (CNC) machining: The CNC machining process utilizes computer software to control and direct the movement and motions of machine tools across the surface of a workpiece. It enables the design and manufacture of highly precise and accurate aluminum CNC parts and products.
• Swiss screw machining: Swiss screw machining is a good option for producing small (but highly precise) cylindrical parts made from aluminum, including electronic or medical fasteners and components.
• Milling (vertical/horizontal): The milling machining process utilizes rotating cutting tools to remove material from the workpiece. It can be vertical or horizontal. Vertical milling machines are best used for small quantities of simple parts, while horizontal tabletop milling machines are best suited for large quantities of complex parts.
• Electrical discharge machining (EDM): EDM uses the electrical discharge between two electrodes to remove material from the workpiece. EDM is typically used for harder and more difficult to machine materials; however, it can be a potential process for all electrically conductive materials–including aluminum.

Why Can Aluminum Machining Be Challenging?

If you were making completely disposable “brackets” for Farmer Joe, it really wouldn’t matter how efficient you are at removing material. But, if you are producing 10,000 “brackets” a week for Hustler Joe, you are going to want to do it right.

The biggest issue with machining aluminum efficiently is getting maximum material removal rates without blowing something up.

If the material is too hot, aluminum can melt and stick to the tool. In that regard, although it virtually cuts like butter, it will not for long if the aluminum sticks to the tool and you are inadvertently performing friction stir welding rather than machining.

Past minimizing friction, chatter can be a nasty beast when running the machine hard. This is especially troublesome with trying to produce clean looking pockets. OK – enough complaining; let’s get into how you will crush it on the floor.

Cutting Tools for Aluminum Machining

Never, in any circumstance, use a general-purpose cutter for Aluminum Machining. It will work technically, but aluminum is completely different than steel.

Here are a few key points about tooling that should help you make the most of your machine.

Cutting Tool Material

Carbide: That’s hopefully an easy one for you. Even for non-performance applications, carbide will have greater value over high-speed steel in both the costs of the tool over the service life and in surface finish.

Still, there are a few good aspects to know about carbide to help you pair up the perfect tool for the job. The bottom line is we just need to understand what we want from a tool. Aluminum is soft cutting, which means that a tool does not undergo hard impact forces while cutting.

What’s critical is to maintain a razor-sharp edge on the tool. So for that reason, we would want hardness over toughness with material characteristics. There are two factors that impact these material properties; Carbide grain size, and binder ratio.

For grain size, larger grain produces harder material, smaller grain produces a more impact resistant, tough material. For aluminum, the objective is to maintain edge sharpness, so we want small grain size to maintain maximum edge retention.

The other factor is the binder ratio. For carbide cutting tools, the binder is cobalt. This can have a range of 2%-20% cobalt composition. As cobalt is softer than carbide grains, more cobalt is a tough tool and less cobalt is a harder tool. In conclusion, we are simply looking for a carbide cutter with a large grain size and low cobalt composition.

Feeds and Speeds

Many simply view 1000 SFM in the equation and set the RPM’s at that speed. If that is the case, you aren’t really running any faster than anyone else.

Honestly, somewhere along the line someone recommended 1000-1500 SFM for most cutters, and the truth is that is an acceptable speed to run your spindle at. However, with harmonic testing you can go well above that speed, some 3x. More on that later.

The real meat of the problem is the feed. If you are using a 1/2″ endmill, and feeding at .003″ per tooth, you are wasting your time. For production you should be feeding at least 1% of the cutter diameter per tooth.

So, if you are cutting with a 1/2″ endmill then your minimum feed should be .005″ per tooth. With a rigid set up and short tool, you could realistically double that.

You can exclude from this only your small tools, down to or at 1/8″ and smaller tools. The issue comes down to chip clearance, so with the thinner chips you will need to decrease your feed accordingly.

Common Operations for Aluminum Machining

The following is a list of the common operations that you are going to perform on Aluminum Machining, and a couple of tips that might help you.

1. Facing

If you are doing this with a shell mill, you should definitely use an aggressive rake angle with polished inserts. Your finish will be excellent, and you will be able to really ramp up the RPM.

2. Pocketing

This is something that a lot of guys do wrong. If you use a step over of half the cutter diameter, and half down, you are doing two things wrong:

You are wasting cutter capability. Go nearly full width. My go-to is 95% of the cutter flat. The reason for this is that the cutter is going to be buried on the corners anyway.

So for the corners, I will have to slow down the feed so the tool doesn’t explode from the depth. If you go to a full 100% I can guarantee you will get paper like wafers between cutter passes due to cutter and material deflection.

Also, 50% stepovers are horrible for harmonics when you are roughing at a respectable rate. The impact of the tool pulling into the work piece is at the worst spot possible, slapping in with every tooth, and if I even bump to 65% stepover the chatter goes down drastically.

Another tip is to use a cutter diameter that is slightly smaller than the inside radius of the pocket. If you are cutting 1/4″ rad pockets with a 1/2″ endmill you will have a tendency to gouge the corners with chatter as the tool tries to change direction.

Tools do not instantaneously change direction at speeds we run, and therefore unload cutter pressure . This is what creates those chirping noises.

I will usually ask if I could resize those rads to 0.265″ for clean corners. That slightly reduces the contact area the tool has with the part geometry. The machine could also run that rounded turn more efficiently with the increased feed rate.

Think of a car racing around a track. At a sharp corner, the car would have to slow down to negotiate, at a larger radius, the machine can continue at high speed.

This should nearly eliminate the chirping in the corners, and help make your parts look good.

3. Slotting

For extremely deep slots, I have two options that work well for me: either trochoidal milling to reduce cutter deflection and chatter, or using a stub flute endmill.

I lean toward stub flutes, since the tool is so much stronger and you don’t have any wasted motion as the tool zipps back and forth. Deep slotting is very much one of those applications where it is often worth it to use a specialized tool.

For shallow slotting (4xD and under), there are no special considerations to be made. Just get after it!

4. Drilling

Utilize Sharp Drills. A lot of times, carbide drills aren’t the solution; there’s no point in running an expensive carbide drill if you don’t have the spindle RPM or production volume to warrant it.

As a rule of thumb, just use a 135-degree split point drill and you should be fine. If there’s a web at the point of the drill, you’re heat soaking the cut unnecessarily.

5. Tapping

General-purpose taps technically function, however, taps specifically for aluminum machining are vastly superior. They have a much more aggressive rake angle, which translates to cleaner cuts and less heat.

Secondly, don’t be a wimp with RPM. If you’ve never spun faster than 200 RPM on your machines, you’re wasting time.

Sure, some machines are just old and tired, and they may have too much backlash to cut any faster. Really, you’re not going to be competitive with that machine anyway. The point is, tapping aluminum is an easy job, don’t waste time on it.

How to Get Awesome Surface Finishes on Aluminum

High RPM. It’s not much of a mystery. Crank it up.

Using a finishing tool that’s super sharp, high helix, and has a very aggressive axial rake angle will really help you out to create a shiny surface finish.

One thing I’d note, however, is that you want to be careful not to spend too much time making the part shinier than it has to be. Sometimes, you may just want to make the customer happy and show off, but let’s be clear – there is a difference between shiny and a high Ra value.

It’s really worth taking the time to do your surface finish calculations so you have the max feed rate for your finish cuts. I’ll typically perform the calculations, then decrease that value by about 10% just to be safe. That said lifiting on that edge will mean you’ll be wrong 50% of the time.

Advantages of Using Aluminum in Machining Operations

Aluminum in Machining exhibits several properties that improve its use in machining operations, along with good machinability:

• High strength-to-weight ratio: Aluminum is strong, lightweight, and these properties are important for machined parts associated with high-performance applications such as aerospace and automotive.
• Corrosion Resistance: Aluminum is available in a number of grades with varying levels of corrosion resistance. In machining operations, grade 6061 is one of the most common in use and has excellent corrosion resistance.
• Electrical conductivity: Aluminum has better electrical conductivity (37.7 million siemens/meter at room temperature) than most other commonly machined metals such as carbon steel (7 million siemens/meter) and stainless steel (1.5 million siemens/meter). This property makes machined aluminum parts ideal for electrical and electronic components.
• Surface finish and anodizing capability: Aluminum is suited to a variety of surface treatment and finishing techniques, including painting, tinting, and anodization of components. This property gives manufacturers the opportunity to enhance the functional and aesthetic properties of the machined aluminum part or product.
• Recyclability: Aluminum has one of the highest recyclability rates, allowing manufacturers to reclaim scrap created through machining operations and building materials abandoned from the finished products at the end of their life cycles.
• Cost: Aluminum is less expensive than many other machined materials (i.e., brass, titanium, and PEEK) without compromising performance. Furthermore, aluminium’s excellent machinability creates lower production costs; its low weight leads to lower shipping costs.

As mentioned above, machining accommodates a wide variety of materials, including metal, plastic, paper, and wood.

In addition to aluminum, a few of the many materials that machining utilizes include many metals (e.g., steel and stainless steel) and thermoplastics. Aluminum offers many advantages over many materials, specifically.

If comparing aluminum to steel and stainless steel, aluminum has a significantly lighter material weight and better machinability.

Typical Machined Aluminum Parts

Professionals in industry utilize drones to complete machining jobs to produce many parts and products. These parts have uses in a wide variety of industries, including:

• Automotive
• Aerospace
• Communications
• Electrical and electronic products
• Lighting
• Medical

Examples of many of these products are dowel pins, EMI housings, front panels, light fixtures, medical items, and spline shafts.

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