Friday, October 20, 2006
Scanner drives 5-axis CNC engine porting
Innovative porting technique with digitising routines, gives significant improvement over hand porting and 3-axis machining, allowing exact duplication of optimum IC engine port designs.
For Florida-based CNC Cylinder Heads, certain aspects of engine manufacture just didn't make sense. Why spend thousands of dollars on a precision-machined engine block, crank and pistons, just to bolt on a set of unported cylinder heads with mismatched port volumes and rough wall surfaces inherent to the casting process? For professional engine builders, precisely ported heads mean better engine efficiency and dyno results.
Hand porting is an art form, but from a manufacturing standpoint, it is impossible to identically size each port volume, or to accurately replicate an 'ideal' port design on another head.
It is also time-consuming, often taking a highly skilled person up to 40 hours to complete a set of heads - very inefficient for a high-variety, low-volume porting business.
From a performance standpoint, cleaning up ports by hand does assist flow by reducing restrictions, but the head cannot deliver its full horsepower potential because of mismatched port volumes.
Numerous manufacturers machine heads on 3-axis CNC machine tools, but machining only in 3-axes, leaves tool marks that cross over one another in various directions, requiring hand polishing and blending to smooth surfaces.
Not only does this add time to the process, but it also removes additional material, making the port larger than originally designed.
With these shortcomings in mind, Bob Hudgins, President of CNC Cylinder Heads, developed a system to solve both problems.
Employing a special combination of high-tech equipment, including vertical machining centres (VMCs), custom-built head fixtures with A- and B-axis CNC rotary tables, and specialised CAD/CAM software, he machines aluminum and cast iron heads in five axes simultaneously, producing a mirror-smooth surface finish, without toolmarks, straight off the machine.
But what to do about the duplication dilemma?
For that, Hudgins uses one additional piece of equipment - Renishaw's Cyclone scanning machine A continuous-contact, reverse engineering tool, the Cyclone scans port and combustion chamber wall surfaces collecting dimensional data to produce a 3D wireframe model of the internal features.
A 3-axis system, the Cyclone is fitted with Hudgins own-design thin probe styli and a special fixture that rotates the head in A- (rotation about the X-axis), and B- (rotation about the Y-axis) axes to allow access to hard-to-reach port areas.
From that data, SURFCAM CAD/CAM software creates 5-axis NC code that drives the machine tool through its cutting routines.
After machining and cleaning, heads are ready for immediate assembly.
Hudgins-designed cylinder heads can be found in various enthusiasts' cars, and NASCAR teams, where cars achieve speeds of 200-mph.
CNC Cylinder Heads also sells the 5-axis system as a turnkey package, offering the technology and training for other companies to duplicate and machine heads using this proven method.
The need for duplication comes from two sources - external and internal.
Professional engine builders approach CNC Cylinder Heads to replicate their new port designs and cut them into numerous other castings.
Builders for NASCAR teams may order up to twenty sets at the beginning of each new racing season, but often come back with new designs throughout the season since their R and D is ongoing - requiring a quick turnaround from Hudgins and his team.
CNC Cylinder Heads' in-house engineers are also continuously developing their own port designs on a variety of manufacturers' castings for street performance and racing applications.
After a newly designed head passes various flow bench and swirl meter tests, the Cyclone digitises the finalised design for duplication.
The company has hundreds of port designs and gigabytes of machining programs stored in a DNC workstation, to be downloaded to a machine tool at a moment's notice.
CNC Cylinder Heads sells these heads off-the-shelf, often packaging them with matching cam, intake and computer chip from other vendors, for purpose-built racing or street applications that often raise base horsepower by 40%.
Digitising deep inside a port - in effect, an angled tube - is more difficult than digitising the perimeter of an object.
Hudgins designed a special Cyclone fixture that can be rotated in A- and B-axes manually or by way of servomotors.
This rotation, combined with Hudgins' special thin styli, allows the Cyclone to digitise all areas of the port.
Rotary encoder's register the angular position of the fixture and a digital display shows position to one thousandth of a degree.
Once all port areas that can be accessed from the home position have been digitised, the fixture is rotated by the operator, to allow access to other areas of the head, and the new angular position is noted.
Separate digitised data files, called patches, are stored for each different angular position.
When all areas of the intake port that can be reached from the intake side of the head are digitised, the head is rotated to finish scanning the intake port through its valve opening.
Digitising then begins on the exhaust port through its valve opening, and the complete scanning of the combustion chamber.
It is then further rotated to finish digitising the exhaust port from the exhaust side of the head.
The Cyclone uses Renishaw's Tracecut software to establish the datum, or home position, and to collect the digitised data.
The patches are downloaded into SURFCAM which has a provision for inputting patch angular position.
Having various mirroring and copying features, SURFCAM is used to manipulate and translate the data into 5-axis NC code for all ports and combustion chambers.
Not every port is digitised - typically one combustion chamber, intake and exhaust port, and sometimes an additional exhaust port depending on head configuration.
Accurate to within 50 microns, the continuous-contact Cyclone scans at a rate of 140 points per second, at a maximum scanning speed of 3 metres/min.
A small block Chevy head can be scanned on the Cyclone in a couple of hours.
The NC machining code is loaded into a DNC workstation that stores the program and downloads it to the machine's control.
Not all machine controls have sufficient processing speed or memory to handle the large 5-axis part programs.
Slow program processing may cause axis-lag errors, leading to inaccurate ports.
While not specifying a minimum processing speed, CNC Cylinder Heads has developed a list of recommended VMCs.
Heads can be quickly set up on another Hudgins-designed fixture which holds and positions the head on the machine tool.
An A-axis Nikken CNC rotary table is mounted on a B-axis rotary table to supply the fourth and fifth axes of movement.
The 5-axis NC code simultaneously moves the machine tool in X-, Y- and Z-axes and the rotary tables in A- and B-axes.
Ports can be machined in one set-up, compared to as many as five set-ups for 3-axis machining.
Not only does this provide quicker throughput, it also eliminates cumulative fixturing errors.
CNC Cylinder Heads uses standard ball nose end mills and special back-cutting tools for hard-to-reach port areas.
As with digitising, the tools cannot reach all port areas, so the head must be rotated for access to combustion chambers and ports.
Typically, it takes four hours and two tool passes to machine a NASCAR head, due to the nature of its casting.
Those heads are purposely cast with additional material in port areas so that any port design will fit into the head without leaving walls between ports too thin.
Heads for street cars, cast with less material, can be machined in half the time, needing only one tool pass.
High-compression NASCAR engines require a smoother wall finish compared to lower-compression street-engines.
However, CNC Cylinder Heads doesn't aim for a specific surface finish specification because it is difficult to determine a very accurate reading on cast aluminum due to material porosity.
Rather, he defines surface finish by tool incremental step-over (distance the cutting tool increments into the port after each pass) or cusp measurement (height from bottom to top of cutting groove).
For a NASCAR head, tool step-over may be 0.76-0.89 mm, whereas a street head would be double that - another reason street heads can be machined quicker.
Cusp height is dictated by the tooling chosen, and ranges from 0.005 mm on a NASCAR head to 0.127 mm on a basic street head.
When first developing his system, Hudgins used a 3-axis 'scan-and-duplicate' digitiser that was fitted to one of his VMCs.
With this device, whatever was scanned was machined, meaning the 3-axis cam software drove the machine tool in the same path as the probe.
The probe's path was not always the quickest or most efficient for the machine tool, and whilst the machine tool was scanning, it wasn't cutting metal.
Hudgins found it much more efficient to have a machine tool cutting a head at the same time a stand-alone digitiser was scanning another - very appropriate for high-variety, low-volume work.
Since the Cyclone is a continuous-contact digitising machine, scanning routines can be done much quicker than point-to-point probing on a machine tool, effectively cutting the scanning routine from days to hours.
Whilst it is a precision instrument, the Cyclone's working envelope measures 600 x 500 x 400 mm and it can hold a model weighing up to 225 kg, more than sufficient to support an aluminum or cast iron cylinder head with fixture.
Hudgins offers his proven system to anyone wishing to duplicate his shop's capabilities.
Maintaining a 100% installation success rate, Hudgins packages everything a job shop needs for 5-axis cylinder head machining, except the machine tool, itself.
For a customer's verified VMC, Hudgins matches the Cyclone digitising system with SURFCAM software, special fixtures for both the Cyclone and machine tool, Nikken rotary tables, special thin probing styli, all necessary accessories and training at its Pinellas Park, FL facility.
For Florida-based CNC Cylinder Heads, certain aspects of engine manufacture just didn't make sense. Why spend thousands of dollars on a precision-machined engine block, crank and pistons, just to bolt on a set of unported cylinder heads with mismatched port volumes and rough wall surfaces inherent to the casting process? For professional engine builders, precisely ported heads mean better engine efficiency and dyno results.
Hand porting is an art form, but from a manufacturing standpoint, it is impossible to identically size each port volume, or to accurately replicate an 'ideal' port design on another head.
It is also time-consuming, often taking a highly skilled person up to 40 hours to complete a set of heads - very inefficient for a high-variety, low-volume porting business.
From a performance standpoint, cleaning up ports by hand does assist flow by reducing restrictions, but the head cannot deliver its full horsepower potential because of mismatched port volumes.
Numerous manufacturers machine heads on 3-axis CNC machine tools, but machining only in 3-axes, leaves tool marks that cross over one another in various directions, requiring hand polishing and blending to smooth surfaces.
Not only does this add time to the process, but it also removes additional material, making the port larger than originally designed.
With these shortcomings in mind, Bob Hudgins, President of CNC Cylinder Heads, developed a system to solve both problems.
Employing a special combination of high-tech equipment, including vertical machining centres (VMCs), custom-built head fixtures with A- and B-axis CNC rotary tables, and specialised CAD/CAM software, he machines aluminum and cast iron heads in five axes simultaneously, producing a mirror-smooth surface finish, without toolmarks, straight off the machine.
But what to do about the duplication dilemma?
For that, Hudgins uses one additional piece of equipment - Renishaw's Cyclone scanning machine A continuous-contact, reverse engineering tool, the Cyclone scans port and combustion chamber wall surfaces collecting dimensional data to produce a 3D wireframe model of the internal features.
A 3-axis system, the Cyclone is fitted with Hudgins own-design thin probe styli and a special fixture that rotates the head in A- (rotation about the X-axis), and B- (rotation about the Y-axis) axes to allow access to hard-to-reach port areas.
From that data, SURFCAM CAD/CAM software creates 5-axis NC code that drives the machine tool through its cutting routines.
After machining and cleaning, heads are ready for immediate assembly.
Hudgins-designed cylinder heads can be found in various enthusiasts' cars, and NASCAR teams, where cars achieve speeds of 200-mph.
CNC Cylinder Heads also sells the 5-axis system as a turnkey package, offering the technology and training for other companies to duplicate and machine heads using this proven method.
The need for duplication comes from two sources - external and internal.
Professional engine builders approach CNC Cylinder Heads to replicate their new port designs and cut them into numerous other castings.
Builders for NASCAR teams may order up to twenty sets at the beginning of each new racing season, but often come back with new designs throughout the season since their R and D is ongoing - requiring a quick turnaround from Hudgins and his team.
CNC Cylinder Heads' in-house engineers are also continuously developing their own port designs on a variety of manufacturers' castings for street performance and racing applications.
After a newly designed head passes various flow bench and swirl meter tests, the Cyclone digitises the finalised design for duplication.
The company has hundreds of port designs and gigabytes of machining programs stored in a DNC workstation, to be downloaded to a machine tool at a moment's notice.
CNC Cylinder Heads sells these heads off-the-shelf, often packaging them with matching cam, intake and computer chip from other vendors, for purpose-built racing or street applications that often raise base horsepower by 40%.
Digitising deep inside a port - in effect, an angled tube - is more difficult than digitising the perimeter of an object.
Hudgins designed a special Cyclone fixture that can be rotated in A- and B-axes manually or by way of servomotors.
This rotation, combined with Hudgins' special thin styli, allows the Cyclone to digitise all areas of the port.
Rotary encoder's register the angular position of the fixture and a digital display shows position to one thousandth of a degree.
Once all port areas that can be accessed from the home position have been digitised, the fixture is rotated by the operator, to allow access to other areas of the head, and the new angular position is noted.
Separate digitised data files, called patches, are stored for each different angular position.
When all areas of the intake port that can be reached from the intake side of the head are digitised, the head is rotated to finish scanning the intake port through its valve opening.
Digitising then begins on the exhaust port through its valve opening, and the complete scanning of the combustion chamber.
It is then further rotated to finish digitising the exhaust port from the exhaust side of the head.
The Cyclone uses Renishaw's Tracecut software to establish the datum, or home position, and to collect the digitised data.
The patches are downloaded into SURFCAM which has a provision for inputting patch angular position.
Having various mirroring and copying features, SURFCAM is used to manipulate and translate the data into 5-axis NC code for all ports and combustion chambers.
Not every port is digitised - typically one combustion chamber, intake and exhaust port, and sometimes an additional exhaust port depending on head configuration.
Accurate to within 50 microns, the continuous-contact Cyclone scans at a rate of 140 points per second, at a maximum scanning speed of 3 metres/min.
A small block Chevy head can be scanned on the Cyclone in a couple of hours.
The NC machining code is loaded into a DNC workstation that stores the program and downloads it to the machine's control.
Not all machine controls have sufficient processing speed or memory to handle the large 5-axis part programs.
Slow program processing may cause axis-lag errors, leading to inaccurate ports.
While not specifying a minimum processing speed, CNC Cylinder Heads has developed a list of recommended VMCs.
Heads can be quickly set up on another Hudgins-designed fixture which holds and positions the head on the machine tool.
An A-axis Nikken CNC rotary table is mounted on a B-axis rotary table to supply the fourth and fifth axes of movement.
The 5-axis NC code simultaneously moves the machine tool in X-, Y- and Z-axes and the rotary tables in A- and B-axes.
Ports can be machined in one set-up, compared to as many as five set-ups for 3-axis machining.
Not only does this provide quicker throughput, it also eliminates cumulative fixturing errors.
CNC Cylinder Heads uses standard ball nose end mills and special back-cutting tools for hard-to-reach port areas.
As with digitising, the tools cannot reach all port areas, so the head must be rotated for access to combustion chambers and ports.
Typically, it takes four hours and two tool passes to machine a NASCAR head, due to the nature of its casting.
Those heads are purposely cast with additional material in port areas so that any port design will fit into the head without leaving walls between ports too thin.
Heads for street cars, cast with less material, can be machined in half the time, needing only one tool pass.
High-compression NASCAR engines require a smoother wall finish compared to lower-compression street-engines.
However, CNC Cylinder Heads doesn't aim for a specific surface finish specification because it is difficult to determine a very accurate reading on cast aluminum due to material porosity.
Rather, he defines surface finish by tool incremental step-over (distance the cutting tool increments into the port after each pass) or cusp measurement (height from bottom to top of cutting groove).
For a NASCAR head, tool step-over may be 0.76-0.89 mm, whereas a street head would be double that - another reason street heads can be machined quicker.
Cusp height is dictated by the tooling chosen, and ranges from 0.005 mm on a NASCAR head to 0.127 mm on a basic street head.
When first developing his system, Hudgins used a 3-axis 'scan-and-duplicate' digitiser that was fitted to one of his VMCs.
With this device, whatever was scanned was machined, meaning the 3-axis cam software drove the machine tool in the same path as the probe.
The probe's path was not always the quickest or most efficient for the machine tool, and whilst the machine tool was scanning, it wasn't cutting metal.
Hudgins found it much more efficient to have a machine tool cutting a head at the same time a stand-alone digitiser was scanning another - very appropriate for high-variety, low-volume work.
Since the Cyclone is a continuous-contact digitising machine, scanning routines can be done much quicker than point-to-point probing on a machine tool, effectively cutting the scanning routine from days to hours.
Whilst it is a precision instrument, the Cyclone's working envelope measures 600 x 500 x 400 mm and it can hold a model weighing up to 225 kg, more than sufficient to support an aluminum or cast iron cylinder head with fixture.
Hudgins offers his proven system to anyone wishing to duplicate his shop's capabilities.
Maintaining a 100% installation success rate, Hudgins packages everything a job shop needs for 5-axis cylinder head machining, except the machine tool, itself.
For a customer's verified VMC, Hudgins matches the Cyclone digitising system with SURFCAM software, special fixtures for both the Cyclone and machine tool, Nikken rotary tables, special thin probing styli, all necessary accessories and training at its Pinellas Park, FL facility.
# posted by Medical Information : 1:56 AM
Subscribe to Posts [Atom]
