Putting together experience with CNC machining centers in the field
▌ How CNC Machining Works
1. Looking over technical drawings and process sheets.
2) Putting the right software on the machine tool.
3) Looking over the program header, cutting parameters, and so on.
4) Finding out the machining dimensions and machining allowance for the workpiece for the current job.
5) Putting the workpiece in the right spot and keeping it there.
6) The workpiece must be perfectly level and in line.
7) Making sure the workpiece coordinate system is set up perfectly.
8) Picking the right cutting tools and settings for cutting.
9) Mounting and clamping cutting tools correctly.
10) Safe ways to practice cutting.
11) Watching the machining process.
12) Changing the settings for cutting.
13) Tell the right people right away if there are any problems with the machining.
14) Looking at the workpiece after machining to make sure it is good quality.
Before machining, here are some safety tips:
1) The machining drawings for new molds must meet all requirements and have clear information. The supervisor must sign the drawings for new molds, and all of the fields in the title block of the drawings must be filled out completely.
2) The workpiece must have a "Qualified" label or stamp from the Quality Control Department.
3) After you get the process sheet, check to see if the datum features (reference points) on the workpiece match the datum features (reference points) in the technical drawings.
4) Check the process sheet very carefully to make sure that the NC program meets all of the requirements. The NC Programmer and the production team need to work together to fix the problem if there are any differences.
5) Look at the tools the programmer chose for both roughing and finishing, and make sure they are right for the size and type of material. If any of the tools don't look right, let the programmer know right away so they can fix them. This will make the machining process more efficient and the workpiece more accurate.
▌ Safety tips for holding pieces of work
1) Make sure the clamping blocks (jacks) are in the right place and that the bolts and nuts on the clamping straps stick out the right amount when you clamp the workpiece. Also, make sure that the screws don't hit the bottom of the fixture base when you tighten the corner clamps.
2) For machining, copper electrodes are usually attached to a backing plate. Before putting the assembly on the machine, check the number of copper blanks against the process sheet to make sure they are the same. At the same time, check that the screws that hold the copper blanks to the backing plate are tight.
3) If there is more than one copper blank on a backing plate, make sure that each blank is facing the right way and that the machining process won't cause any problems between the blanks that are next to each other. 4) Use the program sheet to find out how to hold the workpiece in place based on its shape and size. Remember that the sizes of workpieces are usually given as X x Y x Z. Also, if there is a separate drawing of the component, make sure that the picture on the program sheet is the same as the one on the component drawing. Be very careful about how the workpiece is oriented (which side is facing out) and how the X and Y axes are lined up.
5) Before clamping the workpiece, check that its actual size matches the size requirements on the program sheet. If there is a separate drawing for the part, make sure that the sizes on the program sheet are the same as those on the drawing.
6) Before putting the workpiece on the machine, make sure both the bottom of the workpiece and the machine table are clean. Get rid of any burrs or small damage to the surface of the machine table and workpiece by using an oilstone to smooth them out.
7) Check that the cutting tool won't hit the straps or clamps when you put them in place. Talk to the programmer if you need help. Also, if riser blocks are used to hold up the workpiece, the clamps must be placed directly above these blocks to make sure that the force is spread evenly.
8) Be careful when using a vise to hold something. Make sure the cutting tool isn't cutting too deep, or the clamping position will be too high (which could cause a collision) or too low (which could make it hard to hold).
9) The clamping screws must be fully engaged with the T-nuts; partial thread engagement is not allowed. To make a screw longer, the upper and lower screws must each connect to half of the threads on the coupler. You need to use the full length of the thread to tighten the nut on the clamp strap all the way down. It's not enough to just engage a few threads.
10) When you set the Z-axis zero point (datum), be sure you know exactly where the touch-off point is on the program sheet and what the Z-max data is for the workpiece's highest point. After you put the information into the machine control system, check it again to make sure it is right.
▌ Safety Tips for Clamping Tools
1) The tools must be held tightly and securely, and the tool shank must not go too far into the tool holder.
2) Before clamping a tool, make sure it meets the requirements. You should be able to figure out the tool overhang length (extension) by looking at the machining depth on the program sheet. The overhang should be about 2 mm longer than the machining depth value in most cases. However, you should also make sure that the tool holder won't hit the workpiece.
3) If the machining depth is very deep, ask the programmer about using a two-stage clamping method. First, set the overhang to be shorter (for example, half to two-thirds of the total length). Then, when the machining gets deeper, extend the tool even more. This method can help machining work better. 4) It's very important to check things like the cutting depth and the length of the tool needed when using an extended tool holder.
5) You need to clean the tapered mating surface with a cloth that won't leave lint behind before putting the tool assembly on the machine. Cleaning the mating surface inside the machine spindle as well as the machine tool itself is important to keep the machine tool from getting damaged or losing accuracy.
6) The tool tip is usually used to set the tool length, but in some cases, the tool body may need to be used as a reference. When you set the lengths of the tools, always check the process sheet again.
7) If a program stops or needs to be reset before it can continue, make sure that the new cutting depth is exactly the same as the surface that was already machined. As a rule, it's best to start by increasing the cutting depth by 0.1 mm and then making more changes as needed.
8) If you use water-soluble cutting fluid on rotary-type tool heads (like those with threaded assemblies), you should soak the tool head in oil for a few hours every two weeks to keep it in good shape. This keeps the moving parts inside well-oiled and safe from damage.
▌ Safety tips for putting together and lining up workpieces
1) Make sure the workpiece is perfectly perpendicular when you indicate (dial in) it. First, make sure one side (like the top surface) is straight, and then make sure the other side is straight.
2) To find the center of the workpiece (zeroing), you need to do the centering process twice to make sure the result is right.
3) After using a centering probe to find the center, check the calculated center position by comparing the overall dimensions on the process sheet with the specific dimensions on the detailed part drawings.
4) All workpieces must be centered using a standard method. Even if the zero point is at the edge of the workpiece, you still need to use the centering method to find the center. This is to make sure that the machining allowance is equal on both sides. You need permission from the production team to keep going if you only need to reference one edge. After you finish single-edge referencing, don't forget to add the right amount of compensation to account for the radius of the centering probe.
5) The coordinates you put in for the workpiece's zero point (center) on the machine control panel must match the 3-axis center coordinates that are shown on the computer at the workstation.
▌ Safety Tips for Machining
1) If there is too much material on the top of the workpiece and you are using a big cutter to manually mill it away, be very careful not to cut too deeply.
2) The first cut is the most important step in the machining process. You can be sure that there are no mistakes in the tool length compensation, tool diameter compensation, NC program, spindle speed, etc. if you are careful when making this first cut and check all the settings again. This will keep the workpiece, the cutting tool, and the machine tool from getting hurt. 3) Do a test of the program like this:
a) Set the starting clearance height to 100 mm above the highest point of the workpiece. Then, check that the position looks right by eye.
b) Set the "Feed Rate" override to 0% and the "Rapid Traverse" override to 25%.
c) When the tool gets within about 10 mm of the machining surface, stop the machine.
d) Look at the distance left to travel and make sure the program is right.
e) When you turn the machine back on, keep one hand on the "Pause" button so you can stop it at any time. With your other hand, control the feed rate.
f) When the tool gets very close to the surface of the workpiece, stop the machine again. It's very important to see how much farther it has to go along the Z-axis.
g) When the cutting is going well and there are no problems, set all of the control overrides back to their normal settings.
4) After you type in the program name, write down the name that shows up on the screen by hand on the process sheet and compare it to the original program documentation. When you open the program, check that the tool diameter in the program is the same as the tool diameter on the process sheet. In the "Operator Signature" section of the process sheet, write down the file name and tool diameter right away. You can't do this before or after the operation.
5) As a general rule, the NC technician should not leave the machine alone while roughing is going on. If the technician can't help it, like when they need to change tools or help set up other machines, they have to either supervise another member of the NC team or come back every so often to check on the machine.
6) The NC technician should pay extra attention to areas that weren't reached during the first roughing stage while doing semi-finishing work. This is to keep the tool from hitting these parts that haven't been machined yet.
7) Program Truncation: If a program is stopped while machining and restarting it from the beginning would take too long, tell the Team Leader and the Programmer so they can change the program by cutting out the parts that have already been successfully completed.
8) Program Problems: If something goes wrong while the program is running and the technician doesn't know what to do next, they can raise the tool to a safe height so they can watch the machining process. After that, you can choose what to do next.
9) During the machining process, the NC technician may change the feed rate and spindle speed based on what they find, even though the Programmer set these values. But you need to be extra careful when roughing up small copper pieces. The feed rate shouldn't be too high, or the vibrations could make the workpiece come loose.
10) The NC technician must check the workpiece against the drawings of each part while machining it to make sure there are no problems. If there is a difference between the two, machining must stop right away and the Team Leader must be told so they can check for a mistake.
11) When using cutting tools that are longer than 200 mm, you need to be extra careful about the machining allowances, depth of cut, spindle speed, and feed rate so that the tools don't chatter. Also, the feed rate at the corners needs to be carefully watched.
12) If the program sheet says that the operator needs to check the tool diameter, they need to do it carefully and responsibly, and write down the measured diameter. If the measured diameter is outside the allowed range, the operator must tell the Team Leader right away or change the tool.
13) The operator should go to the workstation to check on the rest of the machining program when the machine tool is running in automatic mode or when it is not in use. Before the next job, they should get the right cutting tools ready and sharpen them so they can be used as backups. This will stop the machines from breaking down.
14) One of the main reasons people waste time is because they make mistakes in the process. Some of these mistakes are using the wrong cutting tools, getting the order of machining operations wrong, wasting time machining areas that don't need it or aren't meant for CNC machining, and using the wrong machining parameters, such as too low spindle speeds, "air cutting" (cutting through empty space), too dense toolpaths, too slow feed rates, and so on. If any of the problems above happen, the operator should talk to the programming team or the right people.
15) The operator must watch the cutting tools closely while they are being used to see if they are starting to wear out. Replace worn tools or inserts as needed. After changing an insert, the operator needs to check that the transition boundaries of the machined surfaces are lined up correctly.
