Monthly Archives : July 2019

Detail of aluminum machined parts, shiny surface.

Achieving Maximum Efficiency in Machining Tight Tolerance Parts

The best practices for precision manufacturing come from using computer numerical controlled (CNC) machining. CNC manufacturing uses high-speed, robot-driven machines and specialized cutting equipment in a custom machine shop. A machine shop for CNC manufacturing will have vertical and horizontal milling machines and lathes.

This CNC process can make custom machined parts to meet the exact specifications of the original equipment manufacturer (OEM) parts. Besides precision manufacturing, a CNC machinist can perform prototype machining in preparation for full-run CNC manufacturing.

This is a guide to the best practices with practical tips on how to create designs, use prototype machining, and choose materials that result in the most cost-efficient custom machined parts produced by CNC machining.

It Starts With Superb Design

Before the machine shop work can begin, creating a precise computer-aided design (CAD) model is the first step. Then, the CAD model is loaded into computer-aided manufacturing (CAM) software. This creates the instructions that tell the robotic machines how to move in order to cut away material from a manufacturing blank in order to form the desired end result.

The instructions are very detailed and include the following:

· The tool paths that are necessary, based on the geometry of the finished part.

· How fast the cutting machine should move.

· How fast and in what direction to turn the materials stock and/or the cutting tool.

· The precise locations and how to move, based on a three- or five-axis coordinate system.

The computer controls of the machine doing the cutting work guide the movements on all three X, Y, and Z axis simultaneously, making complex cuts and detailed geometric patterns possible.

Choosing the Right Cutting Tool for the Design

A CNC lathe has a fixed cutting tool and the material stock rotates. A CNC mill is the opposite, With a mill, the tool rotates and the material stock is stationary. Using a CNC lathe produces a better result for complex cylindrical shapes.

If a part requires square features, these are better made using a CNC mill. If a round part has a square feature, then first the round geometry is produced on a CNC lathe and then the square features are cut with a CNC mill.

Part sizes are limited to the tool clearance of milling machines and the depth of the cuts possible. Lathe part size capability depends on the build space. A live tooling lathe combines CNC milling capability within the lathe, which is a beneficial tooling solution to increase the features that can be produced and reduce lead times.

Default Tolerances

Unless a customer provides specifications that include tolerances, the general permissible tolerance levels are plus or minus 0.005 inches for metal parts and plus or minus 0.010 inches for plastic parts. The walls of metal parts are a minimum of 0.030 inches thick. The walls of plastic parts are a minimum of 0.060 inches thick.

The best practice is to mill the finish to a maximum 125 micro-inches as measured by the root-mean-square (RMS) of the peaks and the valleys of the surface. Surface finish treatment is only applied if requested.

Tighter Tolerances

Very tight tolerances are possible that exceed the standard default tolerances. However, tighter tolerances result in added expense because a tighter tolerance may increase waste, require more fixturing, and/or additional measurement processes. Longer cycle times may be necessary to slow down the machining in order to achieve tighter tolerances. Therefore, tighter tolerances should only be specified when necessary to achieve critical design specifications.

Material Choices and Blank Size

Raw material selection is determined based on the part’s design, functionality, and cost limitations. There is usually a need for certain material characteristics such as chemical resistance, rigidity, thermal stability, heat treat-ability, hardness, and others.

The type of raw material used strongly influences the cost of the part. Plastics are preferred and are much less expensive. Plastics are a wise choice if the rigidity of metal is not needed. Metals that are softer, such as brass and aluminum, are easier to machine than stainless steel and carbon steel.

As a general rule, add 0.125 inches to the material size in all three directions of width, length, and depth. This is the necessary size of the material blank to be used for cutting. It is more cost effective to used standard material blanks if possible. For example, if a part can have the dimensions of 0.875 inches or less on each side, then a standard one-inch cube as the material blank can be used.

Part Complexity — Three-Axis vs. Five-Axis Machining

Two-axis cuts are the easiest and least costly. For a more contoured part, three-axis cutting is necessary with the cuts being made by the tool or blank moving simultaneously on the X., Y, and Z axis.

With five-axis machining more complex parts can be made in a cost-efficient way. In five-axis cutting, the tool and the blank move simultaneously around in five ways. Five-axis machining reduces the number of setups needed, achieves faster cutting speeds, uses better tool paths, and results in a better surface finish.

Fillets

A CNC milling machine (horizontal or vertical) makes interior vertical walls with a radius. It is a round tool, which spins at a high revolution per minute (RPM) that removes the blank material. This limits designs to allow for where radii occur.

Inside corner fillets are easier to make by using a radius that is non-standard. End mills need clearance to turn and to continue milling. By adding 0.02 inches to an internal radius, the cutter can turn slightly without having to stop. This reduces cost and results in better CNC parts. In general, the larger the radius the lower the cost.

Floor fillets are easier to machine if the floor radius is less than the corner radius. If the floor and wall radius is the same size, then it makes it challenging to remove the corner material. If the floor radius is somewhat smaller than the wall radius, then the same tool can be used to create a nice flow through the corner.

Undercuts

If a standard machining tool cannot reach an area, this creates an undercut region on a part. It is better to avoid the need for a special tool that would be required if the feature is not a standard dimension because a custom tool is expensive. A standard tool is less than half the cost of a custom tool. It is also important to make sure the undercut can be reached and is not too deep. A less shallow undercut is better.

Threads

To reduce costs, use standard thread sizes and the largest thread size possible. Small taps have a greater chance of breaking during production than larger ones do. Only specify the depth of the tap necessary because deep, threaded holes increase the cost of the part. A custom tool may be needed for very deep holes.

Surface Finishes

The standard milled finish is 125 RMS. With this finish, minor tools marks may be visible. Smoother finishes of 63 RMS, 32 RMS, or 16 RMS are possible, but they increase the processing time necessary to make the part.

A bead-blast finish creates a matte surface by blowing tiny glass beads under pressure at the surface. If the masking of some areas from the bead blasting is necessary, this adds to the expense.

A corrosion-resistant finish can be created by anodizing a metal part. This can be done with a transparent finish or in different colors (red, black, gold, etc.). This is a popular finish for aluminum parts. Hard-anodizing is also available that creates a thicker, wear-resistant surface layer.

A powder-coat paint finish is created by spraying on paint and then baking the painted part in an oven. This creates a very strong finish that is wear- and corrosion-resistant. It is more durable than regular paint. Many colors are available to create a nicely-finished look for a part.

Custom finishes are also available, at additional expense, such as plating or specialized chemical films.

Summary

By following these best practices as a guide, it is possible to get excellent results when working with Tag Team Manufacturing. This is a machine shop Denver has that can produce up to 50,000 components annually for Denver manufacturing and other locations. Contact Tag Team Manufacturing for a quote from the best Denver CNC machine shop.

CNC Machinist

What you can Expect from a Career in CNC Machining

At some point in his or her life, everyone has to make a decision as to what they want to be when they grow up. It is not uncommon to continue to ask oneself that question into adulthood. If you’ve ever wondered what it would be like to be a CNC machinist, we are here to lay it out for you.

According to the Bureau of Labor Statistics, there are nearly half a million CNC machinists working in the U.S. That number is expected to stay level through at least 2026. If you’re someone who likes to get your hands dirty, to really get in there and find practical solutions to problems that perplex others, a career as a CNC machinist may be precisely what you’re looking for. If you’d rather be working outside or in a custom machine shop setting than sitting behind a desk, read on. There are a number of things about CNC machining that are likely to appeal to you.

This list represents some of what you can expect to experience as a CNC machinist:

You can expect to learn on the job. Although some CNC machinists are trained at vocational schools, community colleges, technical colleges, or through an apprenticeship program, it is still common for companies to create their own training program for the CNC machinists who will be working for them. That’s because most corporations have a very specific manner of doing things, operational procedures that are not taught in other settings. If you’re someone who gets a thrill out of learning new things, the ability to learn on the job may be of benefit to you.

You can expect to be creative. Anyone who has ever worked in manufacturing, whether they were making baseball bats or secret parts for the Pentagon, knows that things can turn a little frantic when anything goes wrong. Every company is beholden to their customers and must follow strict guidelines and delivery dates. If a part is so much as a thousandth of a centimeter off, it can spell peril for the manufacturer. That’s where you come in. CNC machinists are commonly called upon to get to the root of a problem and come up with a creative way to solve it. If you’re a person who has always enjoyed puzzles, or someone who simply likes a good mystery, this job will offer you plenty of opportunities to think creatively.

You can expect to be part of a team. Teamwork is what it’s all about in this job. People count on you and you count on them to make the most of your workday. Whether operations are running smooth as silk or the sky is falling, and upper management is losing their collective minds, CNC machinists work as a team with every other employee in the company. As a CNC machinist, you can expect people to come to you on a regular basis to ask for your opinion and expertise. In turn, you can ask someone else for help when you need it. For some, it’s the camaraderie that makes the job so enjoyable.

You can expect to be know your value. What you do as a CNC machinist is so foundational to your company’s ability to operate that your absence would present a problem. At some point in their live, most people have had a job in which they felt invisible and unimportant. Nothing could be further from the truth for a CNC machinist. Without them, a business would have no way to control quality, and would be far less likely to come up with new innovations.

You can expect to channel your inner Nikola Tesla. As a CNC machinist, you will be part problem solver and part innovator. What commonly happens in the midst of a manufacturing snafu is that innovations are born that can prevent the problem from arising again. You would be the person expected to come up with innovations that work. Everyone has to start somewhere, but the more you innovate, the more confident you become. CNC machining is a job that allows you to try new things until you come across the one that works. And really, that’s how all great inventors got their start.

You can expect to change.  Not everyone is adaptable, not everyone can shift the way they operate. Because of the nature of their jobs, CNC machinists become supremely adaptable, able to veer from the task in front of them to another when it suddenly becomes a priority. If you aren’t especially adaptable going into the job, you can expect to learn the skill out of necessity.  Adaptability is a trait that carries over into every other area of your life and will stay with you into retirement. In an ever-changing world, the ability to adapt is priceless.

You can expect your skills to be sharpened. Just as a prize fighter become stronger through sparring, your work as a CNC machinist will hone your mental skills. Each day, you will learn something new. Each frustration (and there are frustrations) will bring with it a chance to problem solve. Every level of company hierarchy that you interact with will teach you more about how a corporation works. Through this one job, you will grow intellectually and socially. If, at some point, you find yourself moving to a new company, you will find that you can use what you learned through your first experience as a CNC machinist.

You can expect to be on the cutting edge of technology. Computer Numerical Control (CNC) machines are a blend of digital and physical technologies. In this field it is computers that provide instructions to tools of the trade, such as lathes. For example, it is a CNC machine that allows for the precise shaping of raw materials like plastics or metals. Computers are used in every step of CNC machining, and as a CNC machinist you are the person who is counted upon to understand what’s going on with each step and to troubleshoot in order to keep operations running smoothly. Your computer skills and the desire to learn more are essential for success.

You can expect every day to be different. There is no typical workday for a CNC machinist, primarily because it’s impossible to predict when troubleshooting will be needed or when engineering will change plans midstream. There is very little risk of boredom in this job, a benefit for anyone with a curious mind.

Each person on this planet has a different skill set and different goals that drive them. What most have in common is a desire to spend their workdays doing something that has purpose and offers a sense of fulfillment. If you find that CNC machining sounds like something that would fulfill you, why not take a deeper dive and learn more?