CNC machining design and numerical control programming of end cap parts

Abstract: The end cap component is one of the important structures for mechanical support connection. It has many types of components, high production cost and low efficiency. This is a typical end cap type part and its machining is a typical milling process. To meet the requirements for small-scale batch production, simplification of processing routes must be carefully considered to reduce costs and improve efficiency. “Considering multi-tool machining, CNC milling machines choose automatic tool change. One-shot machining speeds up the tool and completes as soon as possible.
The main task of Nc process design is to create a machining program that is also a preparation for Cnc Machining. The program is adjustment components, walking knife paths, dimensions and machine movements. Therefore, it is a instructional process document for CNC programmer performance, manufacturing process and operation method. The NC processing program is a CNC regulatory document. The CNC machining program should include not only part of the process, but also the selection of cutting parameters, motion modes, tooling systems, cutting specifications, and geographic features. Reasonable settings in the process program have a significant impact on programming, machine tool processing efficiency and part machining accuracy. Therefore, the CNC machining process must be carefully and clearly described according to the general process principles combined with numerical control characteristics. Analysis of specific sub-drawings, processing equipment, tools, tool selection, cutting speed, feed, and other parameters and designs optimize the number of reverse selections, part programs to develop parts CNC machining techniques, Written according to the machine selection instructions.
Keywords: CNC machining, CNC technology, NC program

Chapter 1 CNC machining process for end cap parts
2.1 Process analysis of CNC Machined parts

Abstract: The end cap component is one of the important structures for mechanical support connection. It has many types of components, high production cost and low efficiency. This is a typical end cap type part and its machining is a typical milling process. To meet the requirements for small-scale batch production, simplification of processing routes must be carefully considered to reduce costs and improve efficiency. “Considering multi-tool machining, CNC milling machines choose automatic tool change. One-shot machining speeds up the tool and completes as soon as possible.
The main task of Nc process design is to create a machining program that is also a preparation for CNC machining. The program is adjustment components, walking knife paths, dimensions and machine movements. Therefore, it is a instructional process document for CNC programmer performance, manufacturing process and operation method. The NC processing program is a CNC regulatory document. The CNC machining program should include not only part of the process, but also the selection of cutting parameters, motion modes, tooling systems, cutting specifications, and geographic features. Reasonable settings in the process program have a significant impact on programming, machine tool processing efficiency and part machining accuracy. Therefore, the CNC machining process must be carefully and clearly described according to the general process principles combined with numerical control characteristics. Analysis of specific sub-drawings, processing equipment, tools, tool selection, cutting speed, feed, and other parameters and designs optimize the number of reverse selections, part programs to develop parts CNC machining techniques, Written according to the machine selection instructions.
Keywords: CNC machining, CNC technology, NC program

Chapter 1 CNC machining process for end cap parts
2.1 Process analysis of CNC machined parts
2.1.1. Part shape and feature analysis
This part is a typical end cap part consisting of an outer surface, a stepped cylinder and a through hole, which is mainly used for milling, drilling, machining processes, machining centers, CNC milling or controlled drilling parts. ..

2.1.2. Accuracy analysis
Dimensional accuracy:
Higher accuracy requirements mainly include Φ40H6. The dimensional accuracy requirements ensure the correct tool settings during machining, the correct selection of tool wear, and the appropriate selection of the appropriate machining process.

Surface roughness:
The roughness of the main surface roughness of the intermediate holes was 1.6 μm or more, the minimum roughness of the two side walls was 3.2 μm, and the rest was 12.5 μm. Surface roughness requirements are primarily guaranteed by choosing the right roughing and finishing routes, and choosing the right amount of cut and other measures.

2.2 CNC machining process design
2.2.1. Selection of positioning criteria
Starting with ensuring the accuracy of workpiece machining, the positioning reference should select the correct datum and then the coarse datum. Choosing the correct criteria basically guarantees machining accuracy and workpiece mounting. The selection principle includes the principle of duplication of reference, the principle of unification of references, the principle of self-reference, the principle of cross-reference, and the principle of simple tightening.

Keyway Milling Cutter By selecting the rough cutting standard, a sufficient machining margin is secured on the machined surface. Particular attention is paid to adapting the position between the machined and unmachined surfaces to the requirements of the pattern to obtain a fine base as soon as possible.
The selection principle consists of selecting the most important surfaces, raw surfaces, and minimum machining allowances as coarse criteria.
Therefore, the end cap member is selected with the upper surface as a rough reference and the lower surface as a fine reference.

2.2.2. Determine the processing order
Placement of cutting sequence: First, reference: First machine the surface as a precise reference, then position the surface with a fine base.
First planar backhaul: First, the positioning surface and the end face of the hole are machined. Post-machined holes facilitate workpiece positioning and clamping, are stable and reliable, ensure hole and surface positioning accuracy,
First coarse and fine: High processing at the tip of the neck (subjective demand, semi-fine processing)
The first major similar secondary: the main prior court advanced before the main superficial general refinement by a ruling submitted by the court to the court.
Consolidation point paper structure construction analysis, industrial classification origin and processing paper origin origin, rudimentary establishment 33 processing plan.
From time to time:
(A) Part 1 Processing Calculation:
Top surface of milling ――Limited bottom of milling ――Center hole for Drill   hole ――Pig iron side Φ22 ――Intermediate hole for Drill
(2) Second treatment plan:
Grind the top surface-Grin the bottom surface-Drilled center hole-Rough drill center hole-Enlarged center hole-Thick hinge center hole-Thin hinge intermediate hole-Side of the drilled hole-Φ22 on both sides of the milling Hole Burr.
(3) Third treatment plan:
Milling top surface ―― Milling center hole ―― Drilling on both sides ―― Drilling center hole ―― Drilling on both sides ―― Expansion of center hole ―― Thick hinge center hole ―― Fine hinge intermediate hole ―― Both sides of milling hole ―― Deburring.
To summarize the above three options, the first option has both the tool concentration principle and the roughing principle.

2.3. Determine the type of blank and the size and tolerance of the process
The structure of the part is simple, casting blanks can be selected, and the specific values ​​of process dimensions and tolerances are:
(1) For the top and bottom surfaces, the references do not match, so they are selected according to the process dimension chain method.

2.4. Determine total machining allowance and blank size
According to the blank type and processing method, the blank size is 160mm, 100mm, 40mm, 22mm, R20mm, R30mm, Φ60mm and the margin of error is IT13. The rough numbers are:

2.5. Work clamping and positioning method determination
1) Unify design process benchmarks and programming calculations as much as possible
2) Minimize the number of tightening operations and process as many machined surfaces as possible after clamping.
3) Do not use clamping procedures that require long manual adjustments
4) The point of application of the clamp should be that the rigidity of the part drops to a better position. The outer surface of the surface is 60 degrees, and the steps and gaps are tightened by flat jaws. Milling is a contouring process that uses a two-hole positioning method.

2.6. Determine the cutting amount for each process
Determines cutting depth, feed rate, cutting speed, and spindle speed. When choosing the amount of cutting, taking full advantage of the performance of the cutting tool and machine, with the premise of ensuring machining quality and tool durability, maximizing cutting efficiency and minimizing processing costs. With a fixed tool life, cutting speed has the greatest impact on productivity, feed speed is second, and knife consumption is minimal.
Therefore, the cutting amount selection principle: first select the maximum cutting depth, select the maximum feed amount, and finally select the maximum cutting speed.

(1) Selection of cutting depth:
Depending on the machining allowance, the cutting process is usually roughing, semi-finishing and finishing, and each process has different choices. For rough cutting (surface roughness ≥ 12.5), remove as much excess as possible under acceptable conditions. For medium-sized power machines, the cutting depth can reach 8-10 mm, but for machining allowances, a single pass will result in insufficient machine power and tool strength. Also, if the tool is significantly affected by vibrations due to uneven margins or the impact of the tool, it is necessary to use multiple paths. If the tool is split into two paths, the first depth of cut should be as large as possible, typically about 2/3 to 3/4 of the cutting margin. The second cutting depth should be as small as possible and should typically be about 1/4 to 1/3 of the machining allowance.
(2) Selection of feed rate: The tool selects a look-up table according to the hardness of the part material.
(3) Selection of cutting speed: Determine the cutting depth, feed amount, tool life, and determine the cutting speed.
(4) Spindle speed mainly depends on cutting speed.
Face milling cutter
In summary, the amount of disconnection for each process is as follows.
1) Milling base surface
Choose a machining center vise clamp and a carbide face milling cutter.
Ap = 4mm f = 40mm / min Vc = 70m / min nc = 180r / min
2) Drill a Φ13 hole
Select a drill bit for machining center vise clamp φ13
Ap = 23mm f = 30mm / min Vc = 20m / min nc = 500r / min
3) Surface milling
Select one hole and two holes in the machining center. Carbide face milling cutter
Ap = 5mm f = 40mm / min Vc = 70m / min nc = 180r / min
4) Milling 60 outer circle
Select one hole and two holes in the machining center. Carbide end mill
Ap = 0.5mm f = 25mm / min Vc = 70m / min nc = 360r / min
5) Drill Φ40 hole
Select a drill bit with two holes on one side of the machining center
Ap = 41mm f = 40mm / min Vc = 23m / min nc = 200 / min
5) Milling Φ40 hole
Select one hole and two holes in the machining center. Carbide end mill
Ap = 0.5mm f = 25mm / min Vc = 70m / min nc = 360r / min
6) 22 sink milling diameter
Select one hole and two holes in the machining center. Carbide end mill
Ap = 0.5mm f = 25mm / min Vc = 70m / min nc = 360r / min
7) Thin Φ40 hole
Select one hole and one hole in the machining center to place the Φ40 boring knife
Ap = 41mm f = 40mm / min Vc = 74m / min nc = 600r / min

2.8. Tool selection and tool card development
Key considerations for the tool of choice include workpiece material, tool material, amount of cutting, process system stiffness, and other process conditions and machine power.
2.8.1. CNC milling cutter
When choosing a tool, the size of the tool must match the surface size and shape of the workpiece to be machined.
At the same time, different milling cutter parameters are selected for machining, depending on different workpiece materials and machining accuracy requirements.
To machine larger flat surfaces and larger step surfaces, you need to choose a face milling cutter.
A vertical milling cutter should be used to machine planar contours, grooves and small step surfaces.
The mold cutter must be selected for machining spatial surfaces, cavities or punched surfaces.
To machine a closed keyway, you need to select a keyway milling cutter.
You need to select an angled cutter to machine the variable angle surface of the variable angle component.
3D contours and variable bevel contours, ball cutters and drum cutters are often used.
In order to machine various straight or curved grooves, it is necessary to select bevels, special holes for forming tools.
Milling cutter
1) Chip breaker shape selection:
There are three types, L, M, and H, and the M type is selected.
2) Selection of the number of teeth:
Coarse teeth: Suitable for roughing and cutting of soft materials and wide edges. When the power of the machine is low, rough cutting is usually used for stable cutting.
Intermediate tooth: This is a versatile general purpose system with high removal speed and cutting stability.
High Density Teeth: Mainly used to cut large feed rates of cast iron, aluminum alloys and non-ferrous metals
Non-uniform spacing: Used when the cut is stable to prevent resonance in the process system.
Select the coarse teeth in this area.
3) Select a lead angle:
The lead angle of the milling cutter is formed by the insert and body, and the main inclination has a great influence on the radial cutting force and cutting depth. The rake angle is proportional to the radial cutting force. The magnitude of the radial cutting force directly affects the force of the cutting shaft and the vibration resistance of the tool. The smaller the spindle of the tool, the smaller the cutting force in the radial direction, the better the vibration resistance, but the smaller the depth of cut.
The main cutting angle used for this part is 90 °
4) Milling cutter diameter selection:
The diameter of the face milling cutter is mainly selected according to the width of the workpiece.
At the same time, consider the force of the machine, the position of the tool, and the form of contact between the teeth and the workpiece. Spindle diameter can also be used as a basis for selection. The diameter of the face milling cutter can be selected according to D = 1.5d (d: spindle diameter). In general, the diameter of the face milling cutter should be 20% to 50% larger than the cutting width.
Milling cutter diameter D = 80mm, length L = 220mm
The choice of end mill diameter should primarily consider the size of the workpiece and ensure that the power required by the tool is within the rated power of the machine. Small diameter end mills primarily consider whether the maximum speed of the machine can meet the minimum cutting speed requirements of the tool. End mill selection (GB1110-85), end mill diameter D = 10mm, length L = 72mm

2.8.2. Drill bit
Standard twist drill:
The cutting part has two main cutting edges, two small cutting edges, one chisel edge and two spiral grooves.
When drilling a hole in a machining center, the effect of the asymmetric cutting force acting on the two cutting edges can cause drilling deviation due to the lack of a drilling guide in the jig. Therefore, the two cutting edges of the drill bit must have high sharpness.
Carbide Drill Shank Twist Drill (GB1436-85) Diameter D = 13mm, Length L = 151mm
Carbide Taper Shank Twist Drill (GB1438-85) Diameter D = 38mm, Length L = 349mm Carbide Taper Shank Creamer (GB1141-84) Diameter D = 39.6mm, Length L = 349mm.

2.8.3. Center drill
Mainly used for hole positioning. Due to the small diameter of the cut, a higher rotational speed should be selected when drilling the center hole.
Type A center drill (without guard cone): If the hole diameter of the machining center is d = 1 to 10 mm, type A is usually used.
B type center drill with guard cone: When machining a center hole with a diameter of d = 1 to 10 mm, the machining becomes longer and machining accuracy is required. Type B is commonly used to avoid damage to the 60 degree centering cone.
Type C: Threaded Center Drill;
R-shaped circular center drill: When machining with a diameter d = 1 to 10 mm and relatively high positioning accuracy (circular brooch, etc.), use the R type. Parts are selected from Type A center drills with guard cone diameter D = 2 mm and length L = 220 mm.

2.8.4. Reaming drill
Used in machining centers.
Reaming accuracy can reach IT9-IT8 and surface roughness can reach 1.6-0.8 μm.
Tapered shank creamers have a diameter of 10 to 32 mm, and straight shank creamers have a diameter of 6 to 20 mm.
Small hole straight shank creamer diameter 1-6mm; reamer diameter 1-6mm
The processing here is selected from the rigid molding taper shank machine reamer (GB4252-2004) with a diameter of D = 40 mm. Length L = 329mm
Carbide end mill
2.9. Explanation of CNC machining program
The program name is O0002.
N100-N128 is milled on the top surface, starting point is X-146.089 Y-49.998 milling depth Z-3mm
N130-N142 Drill Φ13 Hole Left (Right) Hole Start Point X-60.Y0 (X60.Y0) Drill Depth Z-49
N144-N202 Milling Φ22 groove (left) Starting point X-60.026Y-3.5 (X60.026Y3.5) Milling depth Z-29
N208- N218 Drill Center Hole Φ38 From Tool Point X0.Y0 Drill Deep Hole Z-55
Expanded from Φ38 to Φ39.8 (this program is not posted)
N2028- N2038 Tool point X0.Y0 Hinge center hole Φ40 Hinge depth Z-45