Ultra Precision Machining Solutions for the Automotive Industry

Precitech’s innovative technologies allow many of the main ultra precision applications in the automotive sector. These include Precitech’s high acceleration Fast Tool Servo (FTS) and high speed Levicron milling spindle used to develop freeform shapes on headlamp optics molds.

In order to manufacture Head-Up Display (HUD) molds for aerospace or automotive applications, the Nanoform^® 700 ultra or Nanoform^® L 1000, are ideally positioned to meet users’ needs. When equipped with an HD-160 spindle with a C axis and Adaptive Control Technology (ACT), no other solution in the market today is as suitable for this application.

The Freeform^® L 5-axis machine and the HSK25 quick tool changing system from Levicron^® can be used to make corner cube molds for automotive signal lamp bezels and reflectors. Moreover, Precitech’s long history and knowledge of infrared manufacturing technologies facilitate such automotive IR applications as LiDAR systems for pedestrian/animal detection and self-guiding cars.

Application: Headlamp Optics Molds

Goal:

To show high speed machining of a lens array on nickel plated steel

Process:

Use a Nanoform^® X (Freeform L, Nanoform 700, or Nanoform L 1000) and Fast Tool Servo (FTS500) to machine a collection of concave aspheres on an aspheric nickel plated steel mold for automotive headlamp optics molds

FTS Details:

• Travel: 500 µm
• Peak acceleration: 200 m/sec²
• Typical finish: < 5 nm Ra
• Typical form: < 0.3 µm PV

Part Details:

• Size: 65 x 55 mm
• Material: NiP
• Shape: Concave asphere

Tool Details:

• Rake angle: 0°
• Radius: 0.505 mm

Process Details:

• Coolant: OMS
• Spindle speed: 500 mm/min (constant surface speed)
• Feed per revolution: 4 µm/rev

Results

• Machining time: 3 hours
• Surface finish:
  2.15 nm Rq (0.08 mm Gaussian filter)
  1.74 nm Ra (0.08 mm Gaussian filter)
• Form accuracy: < 1 µm PV
• Cosmetics: Good

Setup photo

Enabling Technology – FTS

Compared to other suppliers, Precitech has more Fast Tool Servo (FTS) systems in use globally. Over the last two decades, Precitech has supplied more than over 500 FTS systems. FTS systems offer a fast technique to fabricate freeform surfaces including: light management micro-structures, lens arrays, toric optics and mechanical features in contact lenses and laser collimators. FTS cutting is usually 10-15 times faster than other servo tool cutting methods (e.g. slow tool servo).

Overview

Three Models	FTS 1000	FTS 500	FTS 70
Travel	1000 µm ≈ 100 Hz 250 µm ≈ 200 Hz	500 µm ≈ 141 Hz 250 µm ≈ 200 Hz 62.5 µm ≈ 400 Hz	70 µm ≈ 100 Hz
Peak Acceleration	200 m/sec2	200 m/sec2	3000 m/sec2
Typical Form	<0.6 µm PV	<0.3 µm PV	<0.3 µm PV
Typical Finish	<9 nm Ra	<5 nm Ra	<3 nm Ra
Servo Band Width	1000 Hz	1000 Hz	900 Hz
FastCom Control System
Operating System:	Windows 7
DSP:	Sharc ADSP
Typical position command update rate:	20 to 35 kHz
D to A converter:	18 bit, ultra-low-noise
Update time jitter:	< 50 ns
GUI:	Windows based UPx style
Two optional packages
Fiducial library – Programing objects defining the cutting path for frequently used fiducial (alignment) marks
20th order aspheric lens arrays with blend zones and on-the-fly tool compensation

 

Precitech FTS units can be incorporated to all Precitech ultra-precision Nanoform and Freeform systems. FTS systems are controlled by Precitech’s exclusive Fastcom III FTS fast command generator.

The Fastcom III control is in two-way communication with the main UPx control. Operators interact totally with the UPx control while FTS programs are functioning. Fastcom is fully supported by Precitech DIFFSYS CAM software. Surfaces can be defined by mathematical expressions, by bitmaps or by point clouds (up to 1,000,000 points).

Benefits of defining a surface by mathematical expression include:

• Tool path commands are produced without interpolation between the lower resolution points in a point cloud resulting in a more accurate surface
• No “point cloud” related restrictions on the size of the surface or on the fine definition of separate features

Enabling Technology – Levicron Spindle

Two configurations of the Levicron spindles are available: ASD-Cx features a pneumatically operated collet system, and, the ASD-H25 features an industry standard, HSK25 interface, enabling the application of an off-the-shelf ultra precision solution for rapid tool changes, and saving money and time. Supplied in 60,000 and 80,000 rpm models, the Levicron spindles allow faster manufacturing and higher levels of quality than other commercial spindles. The low error motions, thermal stability, accurate fast tool changes, long and light shaft design, and powerful bearing system allow for the fast chip-to-chip time and material removal rates needed by highly productive industrial processes.

• Increase productivity and decrease tool expense up to 100,000 rpm and optional HSK25 quick change tool interface
  • Speedily and repeatedly center a tool within 1 µm and no balancing for small tools decreases chip-to-chip time
  • Excels at quick material removal because of high power and strong bearing design
• Enhance surface finish asynchronous error motion less than 30 nm
• Decrease spindle soak time reaches thermal stability in under five minutes
  • Radial growth restricted by integrated symmetrical thin film cooling system
  • Axial growth restricted by self compensating design (bearing cartridge growth in +Z offset by shaft growth in -Z)
• Accurately operated at any speed shaft design guarantee all natural frequencies are outside operating speed range
  • There are no sweet spots

Key Specifications
Speed	60 K, 80 K, 90 K, and 100 K RPM options
Max Shaft Power (configuration dependent)	2.1 - 4.2 kW (2.8 - 5.6 hp)
Axial Stiffness	up to 60 N / µm
Axial Load Capacity	up to 550 N
Radial Stiffness	up to 40 Nm
Radial Load Capacity	up to 330 N
Error motion	Asynchronous error motions less than 30 nm axial

 

Application: Head-Up Display Mold

Goal:

To show the surface finish and form accuracy attainable when machining a Head-Up Display (HUD) mold on either the Nanoform^® 700 ultra or the Nanoform^® L 1000 machine platform using Adaptive Control Technology (ACT) and an HD160 high capacity work holding spindle

Process:

Freeform XZC diamond turning with Adaptive Control Technology to eliminate errors in X and Y that repeat with spindle position

Part Details:

• Material: Brass

Process Details:

• Tool: Single point diamond tool
• Tool radius: 1.5 mm
• Feed rate: 2.5 µm/rev
• Spindle speed: 200 rpm
• Finishing pass duration: 176 minutes
• Coolant: Odorless mineral spirits (OMS)
• Diagonal width: 192 mm
• Z axis excursion: 1.5 mm (twice per revolution)

Results:

• Surface finish near edge: 1.31 nm Ra
• Surface finish near center: 0.744 nm Ra
• Form error: 0.79 µm PV

Status R.M.S. = 0.1127 ( µm) P-V = 0.7869 ( µm)

Part Photo

Setup Photo

Sample 1-near center

Sample 1-outside edge

Enabling Technologies: Large Frame Machines, High-Capacity Spindle, C Axis, and Adaptive Control Technology (ACT)

Users seeking to manufacture Head-up Display molds for aerospace or automotive applications, the Nanoform^® 700 ultra or Nanoform^® L 1000, are uniquely positioned to meet user’s requirements.

When equipped with an HD-160 spindle with a C axis and Adaptive Control Technology (ACT), no other solution in the market today is as suitable for this application.

The dampening and stiffness of the HD-160 results in enhanced surface finish and the capacity for large parts and fixtures. The HD-160 has a definitive load capacity of 170 Kg (375 lbs.) Precitech’s C axis and high resolution encoder, with feedback resolution of 0.010 arc-sec, and servo tuning algorithms allow for tight control of the rotary position of the spindle. The result is the ability to manufacture high accuracy freeform shapes with better surface finish using XZC machining. Finally, Adaptive Control Technology (ACT), solely offered by Precitech, uses a unique learning algorithm to remove errors in X and Z that repeat with spindle position. This allows users to boost the spindle speed, decreasing manufacturing time while enhancing form error.

Nanoform 700 ultra

Nanoform L 1000

• Accommodate heavy and large parts
  HS 160 spindle
• Manufacture non-rotationally symmetric free-form shapes
  Rotary C axis
• Enhance form and decrease machining time
  Adaptive Control Technology (ACT)

Key Machine Specifications	Nanoform 700 ultra	Nanoform L 1000
Swing capacity	700 mm (27.5 in.) dia.	Max swing 1 meter (39 in.) dia.
Surface finish	< 1.0 nm Ra	< 1.25 nm Ra
Form accuracy	< 0.125 micron P-V	< 0.125 micron P-V

 

Following error without ACT active

Following error with ACT active

Applications: Corner Cube Molds

Goal:

To show a multi-tool milling process to machine a corner cube array and automotive reflector applications

Process:

Freeform 4-Axis XYZC milling with HSK25 Quick Change Tooling System. The tools needed to finish the machining process are mounted in separate tool holders. The balance quality and run-out of the tool holders allow them to be altered without having to redo the tool setting process.

Part Details:

• Material: Aluminum

Tool Details:

• Four carbide ball-end mills ranging from 0.3 to 0.75 mm in radius to progressively deepen the corner cube pattern
• One 0.3 mm radius diamond ball-end mill for finishing

Process Details:

• Spindle speed:
  Four roughing passes 16,000 - 50,000 rpm (increasing each step)
  One finishing pass at 60,000 rpm
• Feed rate: 200 mm/min

Machining Time:

Four roughing passes 800 minutes. Total 2170 minutes.

Results:

Optical quality surface and sharp corners on cube

Applications: Ultrasonic Assisted Machining of Steel Mold Inserts

• Material: hardened steel 52 HRC
• Diameter: 30 mm
• Depth: 7 mm
• Surface finish: 1.1 nm Ra
• Form accuracy: 61 nm PV

Enabling Technology: Nanoform^® X with Son-X Ultrasonic Tool Posts

In a number of automotive molding applications, it may be advantageous to use steel given its hardness and heat resistance. The Nanoform X with son-x ultrasonic tool post can directly machining steel molds with a form accuracy of less than 200 nm PV and a surface finish of less than 2 nm Ra. Normally, the extraordinary diamond tool wear experienced while cutting steel has made it hard to use as a mold material. With the ultrasonic tool post, tool wear is comparable to other non-ferrous metals. The dove-tail slide design of the Nanoform X results in greater dynamic stiffness. This enables better surface finish with the son-x device compared to what is attainable on other diamond turning machines.

Enabling Technology – Freeform^® L 5-Axis Ultra Precision Machine

Precitech has incorporated an innovative vertical axis to Ametek field proven large frame platform, enhancing precision and flexibility. With the Freeform L, customers can micro-mill, diamond turn, micro-grind and groove non-rotationally symmetric surfaces. Adding this third linear axis offers users the flexibility to create freeform surfaces which may not be attainable using two linear axis machining.

• Industry leading swing and load capacity
• Flexibility to create freeform geometries with three linear and up to two rotary CNC axes
• Five-axis freedom with three-axis performance Y axis and spindle designed for highest thermal stability
• Thermally controlled enclosure options assure accuracy during long cutting-time parts
• Decreased sensitivity to vibration enabled by its integral TMC MaxDamp^® isolation system
• Capability to create small and large parts auxiliary spindle mount to the X axis

Key Specifications
Turning performance	Surface roughness < 1.5 nm Ra Form accuracy < 0.125 micron P-V
Milling performance	Surface roughness < 10 nm Ra (< 3 nm is achievable with optimum material & cutting conditions) Form accuracy < 0.2 micron P-V
Ultimate load capacity	91 kg (200 pounds) @ 100 psi supply pressure
Standard swing capacity	650 mm diameter over the B axis – can be expanded to 700 mm when equipped with temperature controlled room

 

60 hour stability test using raster flycutting resulting in a 36 nm rms form error 50 mm x 50 mm Nickel Phosphorus)

Y Z turning test resulting in a 0.83 nm Ra surface finish (Nickel Phosphorus)

Enabling Technology – HSK25 Quick Tool Changing System from Levicron

Unable to locate commercially available HSK25 tool holders suitable for ultra precision machining, Levicron formulated a unique process to manufacture their own. They use their ultra precision spindles to grind the tool holders (Refer results below).

UTS-x: Balance Quality G 0.3 mm/s at 60.000 rpm
Industry standard: G2.5 mm/s at 25.000 rpm
UTS-x: Static tool run-out < 0.8 µm TIR
Industry standard: 3 micron TIR

HSK quick change tool interface test at 180 mm from spindle front showing 0.5 micron run-out

Tool Change Repeatablility Test by 4 x 90° Reversal Balancing

Ultra Precision Machining with Automated HSP Tool Change

Form Accuracy Repeatability Test

Process, 60 KRPM micro-milling:

• Insert tool in spindle
• Cut test part
• Correct tool radius, x center, and tool height
• Recut part, form = 0.15 µm
• Remove tool and re-insert, form = 0.1 µm
• Remove tool and re-insert, form = 0.12 µm

This information has been sourced, reviewed and adapted from materials provided by Precitech.

For more information on this source, please visit Precitech.