5 above. Saw cutting the rough stock into blanks would come first. Then the part must be turned on a lathe to create the five-inch diameter and rough turn the diameter for the hexagon. Next a milling machine is used to cut the hexagon and drill the bolthole circle. Before any inspection can be carried out, the part must be deburred. Finally the part can be inspected for accuracy.
The operation sheet is particularly useful when many identical parts are machined (production run). The operation sheet is similar to directions or a how-to approach. The process needed to manufacture the finished part has been decided in advance and is documented for future use.
When small batches of parts are to be made, there may not be an operation sheet. It is the machinist’s responsibility to study the blueprint and decide the necessary steps to machine the part. The operation sheet can aid in this decision making process.
With CNC machining, multiple part geometry features can be performed in one setup. In some cases, when using a CNC Mill Turn Center, a part might be machined to its completed status without ever using another machine. This is very efficient and another advantage of the use of CNC equipment.
To complete an operation sheet, study the blueprint; then decide on the steps necessary to machine the part. Document the machining process and refine any problems the process has, then list the operations in the correct sequence in which they will be performed.
The top section of the operation sheet is for reference information and includes:
The date the document is prepared or revised
The name of the person preparing it
The part name and the part number (from the blueprint)
The quantity of parts to be manufactured
Since some parts may require a large number of operations, it is possible that more than one operation sheet will be needed to document the whole process. The top section also includes a sheet numbering system (Sheet _____ of _____). This information must be included. Other information included on the operation sheet header is the material, the raw stock size for the part, followed by the operations list.
CNC Setup Sheet
The CNC Setup Sheet is the document that tells the machinist what tools are to be used and any specific information related to tools. For instance, it may be necessary to have a certain amount of extension for a drill to be able to completely machine through a part. This document is where the Operator/CNC Machinist finds this information. In Part 5 or 6 of this text you will be introduced to Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) and how you can develop CNC Setup Sheets within the CAD/CAM programs. Many companies today are going to electronic “paperless” factories. The CNC Setup Sheet has two sections. The top section is for reference information and includes:
The date the document is prepared or revised
The name of the person preparing it
The part name and part number (from the blueprint)
The machine being used
Note: If more than one machine is to be used to manufacture a single part, separate setup sheets are completed for each machine.
The CNC part program used in the manufacturing process
Workpiece Zero reference points for the part (program zero)
Work holding devices
Note: If more than one device is needed, the operation number(s) and process are also included.
The lower half of this form lists the tool(s) by number, description and offset. There is a column for comments, remarks or explanations, if needed. Specific tool requirements, like minimum tool length extension, can be entered in the comments section
Quality Control Check Sheet
This planning document is used for the final inspection stage of the machining process. Once the part is completed, it is necessary to check all of the dimensions listed on the blueprint to verify they are within the specified tolerance. The Quality Control Check Sheet is an excellent method to document the results of this inspection and a valuable tracking tool.
Reference information is similar to the other planning documents. Included are:
The date the document is prepared or revised
The name of the person checking the part
The part name and part number (from the blueprint).
On the check sheet, 100 % of the blueprint dimensions and their tolerances are written down in list form. Using this method, sequentially go through each of the print dimensions and log the results. This assures that the machined part meets the specifications given on the blueprint. As the part is checked and verified, some dimensions may not meet specifications. It is important to make sure that these incorrect values are noticed. A good method for relating this is to write those dimensions that are out of print in red ink or use a highlighter pen to emphasize them. You could also include details in the comments section of the QC Check Sheet. If dimensions are found that do not meet specifications, corrective action must be taken.
TYPES OF NUMERICALLY CONTROLLED MACHINES
There are two basic groups of numerically controlled machines, Numerical Control (NC) and Computer Numerical Control (CNC).
In an NC system, the program is run from a punched tape, it is impossible to store such a program in memory. For a punched tape to be used again to machine another part, it must be rewound and read from the beginning. This routine is repeated every time the program is executed. If there are errors in the program and changes are necessary, the tape will need to be discarded and a new one punched. The process is costly and error prone and while this type is still in use, it is becoming obsolete.
Machines with a CNC system are equipped with a computer, consisting of one or more microprocessors and memory storage facilities. Some CNC Machines have hard drives and are network configurable. Program data is entered through Manual Data Input (MDI) at the control panel keyboard, via an RS232 communications interface port or via Ethernet from a remote source like a Personal Computer (PC) network. The control panel enables the operator to make corrections (edits) to the program stored in memory, thereby eliminating the need for new punched tape.
Types of CNC Machines have expanded vastly over the last decade. Turning and Machining Centers are the focus of this book but there are many other types of machines using Computerized Numerical Control. For example there are: Electrical Discharge Machines (EDM), Grinders, Lasers, Turret Punches, and many more. Also, there are many different designs of Machining and Turning Centers. Some of the Machining Centers have rotary axes and some Turning Centers have live tooling and secondary spindles. For this text, the focus will be limited to Vertical Machining Centers with three axes and Turning Centers with two axes. These types of machines are considered the foundation of all CNC learning. All operations
