[Haifeng Process Standards Quick Reference]
The metering accuracy of Haifeng polyurethane equipment depends heavily on the CNC machining accuracy of its critical components. Clearance on one side between a metering-pump gear and its cavity is only 0.005 in (about 0.127 mm). Gear-tooth accuracy and the fit between the gear and housing directly determine volumetric efficiency; any machining deviation can degrade metering accuracy from ±0.3% to more than ±0.5%. During CNC operations, control positioning accuracy within ±0.01 mm and repeatability within ±0.005 mm so that consistent component quality supports the accuracy of the complete machine.
Key process parameters at a glance:
| Parameter | Haifeng standard | Industry reference | Related equipment accuracy indicator |
| Machining-center positioning accuracy | ≤±0.01 mm | ≤±0.015 mm | Metering ratio accuracy ±0.3% (ISO 8060) |
| Repeat positioning accuracy | ≤±0.005 mm | ≤±0.008 mm | Batch-part dimensional consistency CV ≤0.5% |
| Reversal backlash | ≤0.002 mm | ≤0.005 mm | Contour-machining accuracy |
| Spindle radial runout | ≤0.003 mm | ≤0.005 mm | Gear-tooth surface roughness Ra ≤0.4 μm |
| Tool radial runout (solid-carbide end mill) | ≤0.01 mm | ≤0.01 mm | Bore tolerance IT6–IT7 |
| Metering-pump gear-to-cavity clearance | 0.005 in (0.127 mm) per side | — | Volumetric efficiency ≥95%; metering accuracy ±0.3% |
| Metering-pump gear-tooth roughness | Ra ≤0.4 μm | Ra ≤0.8 μm | Tooth wear rate ≤0.001 mm/1000 h |
| Mixing-head valve-core mating-surface roughness | Ra ≤0.2 μm | Ra ≤0.4 μm | Reversing switching time ≤0.3 s |
| Cutting speed for 316L stainless steel | 100–140 m/min | 100–150 m/min | Tool life ≥60 min |
| Cutting speed for aluminum alloy | 200–250 m/min | 180–250 m/min | Dimensional accuracy IT6–IT7 |
| Machining tolerance grade for stainless steel | IT6–IT7 | IT7–IT9 | Interchangeability of critical mating surfaces |
| Hole-position tolerance | ≤0.02 mm | ≤0.05 mm | Assembly accuracy of multi-hole components |
| Machining ambient temperature | 20±2°C | 20±5°C | Thermal-deformation error ≤5 μm |
| Repeat accuracy of in-machine touch-trigger probe | ≤0.002 mm | ≤0.005 mm | Closed loop integrating machining and inspection |
1. Scope
1.1 Applicable operations
This SOP applies to CNC machining of the following precision parts for Haifeng polyurethane equipment:
| Part | Typical material | Key accuracy requirement | Related equipment performance indicator |
| Metering-pump gear | Alloy tool steel/high-speed steel | Tooth-surface Ra ≤0.4 μm; DIN grade 5 tooth profile | Volumetric efficiency ≥95%; metering accuracy ±0.3% |
| Metering-pump body/cavity | Alloy tool steel/9Cr18MoV | Cavity tolerance IT6; cylindricity ≤0.005 mm | Ensures gear-to-cavity clearance accuracy |
| Mixing-head valve core/sleeve | 17-4PH/316L | Mating-surface Ra ≤0.2 μm; cylindricity ≤0.003 mm | Reversing time ≤0.3 s; no internal leakage |
| Servo-motor mounting flange | 6061/7075 aluminum alloy | Mounting-face flatness ≤0.01 mm | Coupling alignment ≤0.03 mm |
| Linear-guide mounting base | Aluminum alloy/carbon steel | Mounting-face flatness ≤0.01 mm/500 mm | Guide-rail parallelism ≤0.02 mm/m |
| Ball-screw support | Alloy steel | Bearing-bore tolerance IT6; coaxiality ≤0.01 mm | Screw axial movement ≤0.005 mm |
| Material-transfer pipeline flange | 316L | Sealing-face flatness ≤0.02 mm; Ra ≤0.8 μm | No leakage at 0.02 MPa in airtightness test |
| Mixing-head nozzle plate | Cemented carbide/tool steel | Hole-diameter tolerance ±0.005 mm; bore-wall Ra ≤0.2 μm | Mix quality and flow consistency |
2. Pre-Job Preparation and Machine Accuracy Verification
2.1 Review technical documents
| No. | Item to check | Accuracy requirement | Acceptance criterion |
| 1 | CNC program | Matches the latest drawing | Program revision matches the process card |
| 2 | Tool list | Includes tool model, geometry, and service-life record | Tool runout measured and recorded |
| 3 | Fixture drawing | Locating datums and clamping plan specified | Locating accuracy ≤0.005 mm |
| 4 | Inspection plan | Includes critical dimensions, tolerances, and tools | Complies with ISO 2768-1 or drawing requirements |
| 5 | Material certificate | Material grade matches the drawing | Includes hardness and composition reports |
2.2 Verify machine accuracy
Calibrate the machining center regularly in accordance with its calibration procedure. Calibration error for critical parameters (spindle runout and positioning accuracy) must be ≤0.005 mm.
| Calibration item | Haifeng standard | Interval | Inspection tool |
| Spindle radial runout | ≤0.003 mm | Quarterly | Dial indicator and master mandrel |
| Spindle axial movement | ≤0.002 mm | Quarterly | Dial indicator |
| X/Y/Z-axis positioning accuracy | ≤±0.01 mm | Quarterly | Laser interferometer |
| X/Y/Z-axis repeat positioning accuracy | ≤±0.005 mm | Quarterly | Laser interferometer |
| Reversal backlash | ≤0.002 mm | Quarterly | Laser interferometer |
| Worktable flatness | ≤0.01 mm/500 mm | Every 6 months | Precision level/straightedge |
| Spindle-taper cleanliness | No residual chips or foreign matter | Every shift | Visual and touch inspection |
2.3 Verify tool accuracy
Tool geometry directly affects dimensional accuracy and surface quality. Radial runout must be ≤0.01 mm for solid-carbide end mills and ≤0.03 mm for indexable-insert tools. Tools for precision machining generally require runout below 3 μm at high milling speeds, with runout below 3 μm along the full cutting-edge length.
| Tool type | Radial-runout limit | Inspection tool | Inspection frequency |
| Solid-carbide end mill | ≤0.01 mm | Dial indicator (supported on V-block) | Before loading each batch |
| Indexable face mill | ≤0.03 mm | Dial indicator | Every tool change |
| Drill/reamer | ≤0.01 mm | Dial indicator | Every tool change |
| Precision boring tool | ≤0.005 mm | Dial indicator and master ring gauge | Every tool change |
| Shrink-fit holder | ≤0.003 mm | Dial indicator and master mandrel | Every tool loading |
3. Structured CNC Machining Workflow
3.1 Pre-shift preparation and machine warm-up
3.1.1 Confirm machine status
Switch on the main power, then start the machine and CNC system. After the system completes its self-check with no alarms, return each axis to its reference point (home). The recommended sequence is Z-axis first, followed by X and Y, to establish an accurate machine coordinate system as the datum for tool setting and machining. After homing, run the machine unloaded at low speed to warm it up. This distributes lubricant evenly over the spindle bearings and guide rails and reduces the effect of thermal deformation. A thermal-error compensation study showed that effective compensation reduced positioning error from −2.53–14.83 μm to −1.47–2.71 μm, an 81.66% reduction.
3.1.2 Check cooling and lubrication systems
Confirm that air pressure is stable within the machine’s specified range (typically 0.5–0.7 MPa) and that lubricant and coolant levels are within their normal ranges. For high-speed spindles, pay special attention to taper cleanliness; no chips or foreign matter may remain. Adjust coolant concentration to the material: use 8%–12% emulsion for stainless steel and 5%–8% for aluminum alloy.
3.2 Clamp the workpiece and establish datums
3.2.1 Control clamping accuracy
Secure clamping directly affects machining safety and accuracy. Before clamping, clean the worktable and workpiece locating surfaces and remove burrs and oil. When using a vise or strap clamps, tighten diagonally and use a dial indicator to align the workpiece parallel to the machine axes. Keep error within the process limit (typically ≤0.02 mm). For precision parts such as metering-pump gears and mixing-head valve cores, use dedicated locating fixtures to improve repeatability.
| Clamping method | Suitable workpiece | Locating accuracy | Notes |
| Precision vise | Small and medium regular parts | ≤0.01 mm | Verify jaw parallelism |
| Vacuum chuck | Thin-wall plate parts | ≤0.005 mm | Check uniformity of vacuum force |
| Dedicated locating fixture | Metering-pump body, mixing head | ≤0.005 mm | Check locating-pin wear regularly |
| Four-axis rotary table | Multi-face machining parts | ≤0.008 mm | Verify rotary center |
3.2.2 Control tool-setting accuracy
Tool setting links the program coordinate system to the physical workpiece. Set each tool independently and enter its compensation value. Verify the origin with the “G54 X0 Y0” command to avoid batch scrap caused by tool-setting errors. Haifeng requires tool-setting accuracy within ±0.005 mm. For critical parts such as metering-pump gears and mixing-head valve cores, use a high-accuracy tool presetter or laser tool-setting system.
3.3 Validate the program and cut the first article
3.3.1 Program simulation and dry run
Before automatic machining, use the CNC graphical simulation or Dry Run mode to check for abnormal tool retraction, undefined axis movement, or possible collision with fixtures. Pay particular attention to whether the G codes at the beginning and end of the program (such as G90/G91 and G17/G18) match the intended operation.
3.3.2 First-article trial cut
Apply a “verify at low speed” approach to the first trial cut. Set the feed override below 50% and enable Single Block mode. After machining the first feature (such as a hole or milled face), pause the machine and measure critical dimensions with calipers, micrometers, or other suitable gauges. If a dimension is out of tolerance, make a fine adjustment through tool-radius compensation or work-coordinate offset. Resume continuous machining at 100% override only after the part passes inspection.
3.4 Cutting parameters and accuracy control
3.4.1 Material groups and cutting parameters
CNC machining for Haifeng equipment mainly involves carbon steel, alloy steel, stainless steel (304/316L), aluminum alloy (6061/7075), and cemented carbide. Select optimized parameters from the applicable table for each material.
Recommended milling parameters for stainless steel (304/316L) (with TiAlN-coated carbide tools):
| Operation | Cutting speed Vc (m/min) | Feed per tooth fz (mm/tooth) | Radial depth ae | Axial depth ap |
| Roughing (side milling) | 100–140 | 0.05–0.08 | 0.10D–0.15D | 0.5D–1.0D |
| Semi-finishing | 120–160 | 0.03–0.06 | 0.05D–0.10D | 0.3D–0.5D |
| Finishing | 140–180 | 0.02–0.04 | 0.02D–0.05D | 0.1D–0.3D |
Recommended milling parameters for aluminum alloy (6061/7075):
| Operation | Cutting speed Vc (m/min) | Feed per tooth fz (mm/tooth) | Radial depth ae | Axial depth ap |
| Roughing | 200–300 | 0.10–0.20 | 0.15D–0.25D | 1.0D–2.0D |
| Finishing | 250–350 | 0.05–0.10 | 0.05D–0.10D | 0.3D–0.5D |
With stable, consistent machining conditions, aluminum alloys 6061 and 7075 can achieve tolerances of ±0.01 mm or tighter.
3.4.2 Control and compensate for thermal deformation
Thermal-deformation error is a key indicator of machining-center accuracy. Apply the following controls when machining Haifeng equipment components:
1. Warm up before machining: Run the spindle unloaded for 15–30 minutes so that spindle bearings and ball screws reach thermal equilibrium.
2. Control coolant temperature: Maintain cutting-fluid temperature at 20±2°C to prevent heat from cutting from expanding the workpiece and tool.
3. Apply online compensation: For long continuous operations, enable the machine’s thermal-error compensation function and correct motion commands in real time using temperature-sensor data. Software compensation is widely used: a temperature-to-deformation mapping model calculates thermal error from live temperatures and applies corrections to motion-control commands.
4. Control ambient temperature: Maintain the precision-machining area at 20±2°C.
3.4.3 Monitor tool wear
Tool wear directly affects dimensional accuracy and surface roughness. Operators must monitor the following during machining:
| Item monitored | Normal condition | Warning threshold | Response |
| Spindle load | Stable without sharp fluctuation | Fluctuation >10% | Check tool/workpiece condition |
| Cutting sound | Even humming | Shrill squeal or dull impact | Stop immediately and check for chipped tool edges |
| Surface-roughness trend | Stable within standard | Ra increase >20% | Replace tool or adjust parameters |
| Chip shape | Regular C-shaped or short spiral | Powder-like or long tangled chips | Adjust feed/speed |
3.5 In-machine inspection and closed-loop machining
For critical precision parts such as metering-pump bodies and mixing-head valve cores, use in-machine inspection to create a closed-loop process integrating machining and inspection. Repeatability of the touch-trigger probe must be ≤0.002 mm.
In-machine inspection procedure:
1. After semi-finishing the part, call the in-machine inspection program.
2. Trigger the probe to contact key measurement points automatically (bore diameter, mating surface, position, etc.).
3. The system compares measured values with tolerance requirements.
4. If a deviation exceeds the warning range, the system automatically corrects the tool compensation value.
5. Perform finishing after correction to ensure the final dimensions pass inspection.
4. Key Parameters for CNC Machining Accuracy
| No. | Accuracy category | Parameter | Haifeng standard | Inspection tool | Inspection frequency |
| 1 | Machine accuracy | X/Y/Z-axis positioning accuracy | ≤±0.01 mm | Laser interferometer | Quarterly |
| 2 | Machine accuracy | X/Y/Z-axis repeat positioning accuracy | ≤±0.005 mm | Laser interferometer | Quarterly |
| 3 | Machine accuracy | Reversal backlash | ≤0.002 mm | Laser interferometer | Quarterly |
| 4 | Machine accuracy | Spindle radial runout | ≤0.003 mm | Dial indicator and master mandrel | Quarterly |
| 5 | Tool accuracy | Solid-carbide end-mill radial runout | ≤0.01 mm | Dial indicator | At each batch tool loading |
| 6 | Tool accuracy | Precision boring-tool radial runout | ≤0.005 mm | Dial indicator and master ring gauge | Every tool change |
| 7 | Machining accuracy | 316L stainless-steel dimensional tolerance | IT6–IT7 | CMM | First article and sampling |
| 8 | Machining accuracy | Aluminum-alloy dimensional tolerance | IT6–IT7 | CMM | First article and sampling |
| 9 | Machining accuracy | Hole-position tolerance | ≤0.02 mm | CMM | First article and sampling |
| 10 | Surface quality | Metering-pump gear-tooth roughness | Ra ≤0.4 μm | Surface-roughness tester | 100% inspection |
| 11 | Surface quality | Mixing-head valve-core mating-surface roughness | Ra ≤0.2 μm | Surface-roughness tester | 100% inspection |
| 12 | Surface quality | General mating-surface roughness | Ra ≤0.8 μm | Surface-roughness tester | Sampling inspection |
| 13 | Critical fit | Metering-pump gear-to-cavity clearance | 0.127 mm per side (0.005 in) | Pneumatic gauge/plug gauge | 100% inspection |
| 14 | Critical fit | Mixing-head valve-core-to-sleeve clearance | 0.005–0.015 mm | Pneumatic gauge | 100% inspection |
| 15 | Environmental control | Machining ambient temperature | 20±2°C | Temperature/humidity logger | Continuous monitoring |
| 16 | In-machine inspection | Touch-trigger probe repeatability | ≤0.002 mm | Master-ball calibration | Every shift |
5. Common Problems and Process Pitfalls
5.1 Excessive tool runout destabilizes bore accuracy
Symptom: Bore dimensions vary within tolerance but the CV exceeds 0.5%, or chatter marks appear on the bore wall.
Root cause: Tool radial runout exceeds the standard. When a solid-carbide end mill has runout above 0.01 mm, the effective diameter of its cutting edges exceeds the nominal diameter and the edges carry uneven cutting loads, resulting in oversized bores and poorer surface quality. In reaming and boring, every 0.01 mm increase in tool runout can cause a bore-diameter deviation of 0.015–0.02 mm.
Corrective actions:
1. Before loading each batch, measure runout with a dial indicator: ≤0.01 mm for solid-carbide end mills and ≤0.005 mm for precision boring tools.
2. Check holder-taper cleanliness and wear; replace the holder if needed.
3. Replace collet holders with shrink-fit holders to reduce runout to below 0.003 mm.
4. For precision bores, separate boring and reaming into distinct operations: rough-bore first, then finish with an adjustable reamer.
5.2 Work hardening during stainless-steel machining causes abnormal tool wear
Symptom: Tool life when machining 316L falls sharply (below 30 minutes), cutting force increases, and surface quality deteriorates.
Root cause: Austenitic stainless steel (304/316L) has a strong tendency to work-harden. During cutting, surface hardness can rise from HB 150 to above HB 300. Incorrect cutting parameters, such as insufficient depth of cut or feed, make the tool repeatedly cut the hardened layer and accelerate wear. The molybdenum content of 316L makes it more prone to work hardening than 304.
Corrective actions:
1. Use a high-feed, shallow-cut strategy so the cutting edge always engages material below the hardened layer.
2. Use trochoidal milling for 316L. Reference parameters: Vc=196 m/min, fz=0.08 mm/tooth, ae=1 mm, ap=24 mm.
3. Select TiAlN- or AlTiN-coated carbide tools to improve resistance to crater wear.
4. Apply sufficient coolant to prevent heat buildup from worsening work hardening.
5.3 Thermal deformation causes precision-part accuracy drift
Symptom: Parts that pass in the morning show systematic dimensional shift in the afternoon (typically 0.01–0.03 mm), or dimensions drift gradually during continuous machining.
Root cause: Cutting and friction heat expand the machining-center spindle, ball screws, and workpiece. Spindle axial thermal growth can reach 0.02–0.05 mm, and ball-screw growth can reach 0.05–0.10 mm over a 3 m travel. For precision parts in Haifeng equipment with tolerances as tight as ±0.005 mm, thermal deformation is a primary cause of batch accuracy drift.
Corrective actions:
1. Run the spindle unloaded for 15–30 minutes before machining; begin only after thermal equilibrium is reached.
2. Enable thermal-error compensation during long continuous runs. Test data indicate that compensation can keep thermal error within 8 μm.
3. Schedule finishing operations during the stable period after the machine reaches thermal equilibrium.
4. For precision parts, use a staged process: rough machining, natural cooling, then finish machining.
5.4 Clamping deformation puts thin-wall parts out of tolerance
Symptom: Thin-wall parts such as metering-pump bodies become oval or out of tolerance after machining, and spring back when the fixture is released.
Root cause: Excessive clamping force or poorly distributed clamping points elastically deform the part while it is held. The tool cuts material from this deformed state; once unclamped, the part springs back and its actual dimensions shift.
Corrective actions:
1. Use a vacuum chuck or dedicated soft jaws instead of hard-jaw clamping to distribute clamping force.
2. For precision thin-wall parts, use axial clamping with auxiliary radial support.
3. After roughing, release the fixture and allow the part to cool naturally; then finish with lower clamping force.
4. Reduce finishing feed as appropriate to limit cutting-force deformation.
5.5 Incorrect coolant concentration causes surface-quality variation
Symptom: Stainless-steel parts made with the same program show inconsistent roughness, with some batches exceeding Ra 0.8 μm.
Root cause: Cutting-fluid concentration is outside the recommended range. Stainless-steel machining needs sufficient lubrication and cooling. Emulsion below 8% provides insufficient lubrication and accelerates tool wear; above 15%, cooling performance declines, foam increases, and chip evacuation worsens.
Corrective actions:
1. Use 8%–12% emulsion for stainless steel and 5%–8% for aluminum alloy.
2. Measure and record coolant concentration with a refractometer every shift.
3. Regularly remove chips and floating oil from the coolant tank to prevent bacterial growth.
4. For precision machining of 316L stainless steel, use high-pressure through-tool coolant (pressure ≥70 bar) to aid chip removal and cooling.
5.6 Incorrect program coordinate setup causes batch scrap
Symptom: The first article passes, but after several consecutive parts a systematic dimensional shift appears, equal to a fixed offset.
Root cause: The work coordinate system (G54/G55) or tool-length compensation value is set incorrectly. In multi-operation machining, failure to switch work coordinates or the correct tool-compensation number makes the tool move from the wrong datum.
Corrective actions:
1. Follow the “tool setting–verification–trial cut” process strictly; set each tool independently.
2. Verify the origin with “G54 X0 Y0” and start batch production only after confirming it is correct.
3. Set a safe height (Z-axis safety plane) at the beginning of the program to prevent a coordinate error from causing a tool crash.
4. Before batch machining, dry-run a complete cycle in Single Block mode and confirm the path is correct.
