The mathematics behind the choice to automate machining operations like milling and turning make financial sense; robots work 24-hours per day with very few sick days; they cut associated labour costs while allowing redeployment of machine tenders; they complete potentially dangerous tasks without the risk of injury; and they offer maximised repeatability. Further, in a period which has seen estimated hourly labour charges double, the real cost of robotics has halved.
According to automation specialist Barr & Paatz, the automated handling of machine tools, parts and materials can maximise the utilisation of existing machining centres, reportedly by as much as 95%. The sentiment is similar at Bosch Rexroth, which says that success in manufacturing is determined ultimately by how fast you can run while armed with the latest technology.
Automotive suppliers and manufacturers are by far the largest consumers of robotic equipment, accounting for approximately 70% of the robots ordered each year. Over 85% of robots shipped to North American companies are destined for use in welding and material handling, but robots are increasingly being used for higher-force applications, including material removal, according to Bosch Rexroth.
Many machine tool builders, particularly lathe manufacturers, are beginning to introduce robots into their model specifications. Index, manufacturer of multi-spindle automatic lathes, has added Stäubli six-axis robots to its latest models, contributing significantly to their performance and flexibility, especially for complex chucked components. Index’s MS52C lathe can be converted into an automatic chucking lathe with the addition of a Stäubli RX60 robot to load blanks for machining and remove finished components, while a RX90 robot can also be added to the larger MS52C. The open-front design of both machines allows the robot to be flange-mounted on the workspace cover. A dual gripper removes blanks from storage in front of the machine before parts are brought to the working spindle and exchanged for finished parts that are then orientated and placed in the exit storage, also at the front of the machine. According to automation supplier Fastems, virtually any make of CNC turning machine can be transformed into an unmanned production centre by retrofitting one of its RPC- 16G robotic cells, which automates loading and unloading of workpieces into and out of the machine spindle. Biglia is also adopting automation on its B745 Y3 and B765 Y3 14-axis CNC lathes: both machines feature an integrated CNC unloading arm that removes finished components from either the main or counter-spindle, provided that the parts have been machined from bar.
Age of the robot
It can be argued that the use of an automated multispindle machine is the most productive means of turning automotive parts in high volume. The one operation/ one index formula has been successful for many years at automotive supply shops around the world, with take-up today remaining high.
A case in point can be seen at DJJ Precision Engineering of Pontypool, UK which has invested in an Index MS32C sixspindle multi automatic. DJJ’s Managing Director, Dennis Jones, says that the new machine has allowed the company to resume production of an automotive job previously lost to India. Machined from high tensile steel bar (606M36), the component is a vehicle braking system shaft for a Tier One automotive supplier in the UK. Operations mainly involve turning outside diameters, thread-cutting and a small amount of prismatic machining to produce a hexagon at one end. Cycle time on the Index MS32C is 14 seconds, which allows the company to manufacture the part for £0.29, plus material and finishing costs. The previous cycle time on a single-spindle, sliding head auto was over four times longer. Another investor in the latest multi-spindle auto technology is Turkey’s Cengiz Makina, which exclusively uses Tornos machines. Founded in 1981, the company manufactures turned parts for diesel and brake systems in the 5-45mm diameter range. “With its multi-spindle machines, Tornos has always been a good solution for high-volume, precision-turned parts,” says a company spokesperson.
Sliding head automatics are also taking a share of this market, as demonstrated by Philidas, based in Pontefract, UK. The company uses its recently-installed Star SV-32 CNC sliding head auto to produce automotive fasteners in quantities totalling millions – previously they were completed on conventional cam-type automatics. CNC Team Leader Steve Webley says that increasingly complex fasteners (some requiring five or six different operations), in combination with competition from the Far East, prompted the investment decision. “The new Star SV-32 is doing the work of six machines, that is, of one single-spindle fixed-head lathe and five multispindle automatics,” he says.
Another UK automotive subcontractor to invest in a new Star is Auto Turned Products (ATP). The company’s SR-32J is the second of its type installed in quick succession at the Northampton-based company. ATP had found that second operations, following conventional turning with existing machines such as multi-spindle automatics, turret-type automatics and fixed head CNCs, had risen to such an extent that single set-up machining on a Star turn-mill centre was needed to maintain competitiveness.
ATP says that one component in particular has resulted in significant cost-of-labour savings and improved quality, specifically the locking feature on wheel nuts supplied to Land Rover and Jaguar, parts used on models suchas the Jaguar XF. Previously produced in two set-ups on a fixedhead CNC lathe and a machining centre, the component is now produced in one cycle on an SR-32J to very high accuracy, despite the toughness of the material.
Automated tool monitoring
Sometimes it is not the obvious form of automation, i.e. component handling, that provides a productivity boost, as UK-based turned parts specialist MSP recently discovered. MSP was experiencing a problem when machining components using Hastelloy bar on a CNC sliding head auto. The material’s toughness was causing unpredictable and early failure of drills and taps, a costly and time-consuming problem. The drill is relatively inexpensive at £5 ($12), but a broken bit in the hole, or a hole that is absent or not drilled to depth will destroy an £80 solid carbide thread milling cutter as it tries to enter. The company selected Emmaco UK to install automated tool monitoring.
Fitted with an acoustic sensor, clamped to the sliding head lathe’s tool platen, the Argotech PA-2 automatically checks the sound frequencies produced during a critical drilling operation, instantly stopping the machine in the event of tool wear or failure.
Says Leroy Lippett, MSP’s Engineering Manager: “Setting up acoustic monitoring is very straightforward. We run a peck drilling cycle on a component using a new tool and record an ideal acoustic profile on the screen of the PA-2. We then draw boundary boxes at strategic points along the trace where it is essential for the drill to be present. These are on the second peck to make sure that the drill does not break during entry, on the last peck to verify that the hole is completely machined and on retraction to warn if the drill breaks on exit. If there is no alarm, it is certain that the hole has been drilled to the required depth and is clear of obstruction, so it is safe for the thread milling cutter to enter. “When the drill does eventually break, the lower threshold of one of the boundary boxes detects the absence of sound and the lathe is stopped instantly,” he continues. “Alternatively, the same boundary box detects when the noise from the drilling operation increases beyond the upper threshold and similarly stops the machine to avert tool breakage and allow its early replacement.”
During a full year of system operation, MSP has not lost a single thread mill prematurely, whereas before the Argotech PA-2 was fitted, the subcontractor was losing £400 in cutters per week (based on 24-hour running of the sliding head automatic). This means that within the first 10 weeks of installing the process monitor, there was a saving of £4,000 ($10,000), equal to the cost of installing the PA-2 and both sensors.
In generic terms, the ongoing demand for automation is forcing many machine tool and robot manufacturers to work co-operatively to develop user-friendly solutions. ABB robotics and Okuma, for instance, have in tandem developed an ABB robot standard interface for Okuma machine tools. This provides operators with a single operating environment, while the interface saves production time and reduces operator training.
Developed on the open PC platform used by Okuma, the interface consists of two parts: the graphic interface; and the extendable robot controller program libraries and configuration files, which enable the programmer to create the code for the robot tending various machines without the need for complex routines.
Manufacturers that venture down the robot route rarely turn back, finding the return on investment and ongoing advantages too good to ignore. An example of this is King Automotive Systems, of Coventry, UK. Six years ago the company installed its first Fanuc robot, for loading castings into a brake disc manufacturing cell. The project saved 50% of operators over three shifts, and King has since installed a total of 11 Fanuc robots, with the latest two lines producing knuckle joints for BMW's Mini and for the Land Rover Freelander.
The Mini line has seven machining centres, with two Fanuc robots loading and two deburring parts, while the Freelander line has three machining centres, with one Fanuc robot loading and deburring. Components are loaded on to a pallet conveyor that positions product in a handling area for the robots to load and unload the joints. Each cell is manned by one setter operator over each of three shifts. Bringing efficient machining processes back in-house has resulted in similarly impressive results at diesel engine manufacturer Perkins, assisted by close partnerships with Fanuc Robotics UK and Heller Machine Tools. Previously machined by an external, non-UK contractor, the Perkins Type 400D engine cylinder head now benefits from a newlycommissioned, fully-automated, in-house machining cell.
Operating a three-shift system over five days, the new system produces 80,000 cylinder heads per year. Pallets of cylinder head castings are delivered to the cell where a Fanuc R2000iA/165 robot equipped with a Fanuc V500iA/3DL vision system identifies the position of the heads before grasping them using a magnetic gripper. After re-orientating the head (using a fixture), the robot then places the cylinder head into a marking machine before placing it on to the machining cell input conveyor.
The vision system allows Perkins to use standard pallets, eliminating the need for special jigs and costly containers. The robot is further utilised by loading finished heads into a leak-testing machine, after which they are reloaded into the pallet.
The machining cell comprises six Heller machining centres – four for pre-machining and two for finish machining. Two washing machines ensure complete removal of metal cuttings. Servicing the machines are two further Fanuc R2000iA/165 robots, mounted on a 20m linear slide. Cylinder heads enter the machining area on a conveyor and from that point are handled only by the robots. The two Fanuc machines are identical and, although programmed to work together servicing the machines, each one is capable of servicing the entire cell independently – therefore providing built-in redundancy if needed. Using a single gripper design, each robot is able to locate the cylinder heads in any of three positions, dependent on the loading/unloading requirement.
It is generally acknowledged that machine loading and unloading is a more complex application than basic material handling, as the robot needs to provide both manipulative and transport capabilities. One of the chief problems for robotic arms is that machine tool working areas are often restricted by the presence of hardware such as chucks, vices, spindles, toolposts and coolant nozzles. To counter such obstacles, Motoman has introduced its IA20 sevenaxis robot, nicknamed ‘the snake’ due to its ability to access restricted spaces.
The robot was seen at a recent machine tool exhibition automatically loading and unloading a Hardinge XV710 vertical machining centre. The robot loaded a hydraulic fitting into the first collet of a Hardinge four-station indexing unit. After the first machining operation, the part was transferred to the three other collets for additional operations before being unloaded.
Other recently introduced robot arm solutions for milling machine tending operations include the ABB IRB 6620LX, a five-axis overhead-mounted robot on a linear axis unit that is said to combine the advantages of an articulated robot and a linear gantry for improved cycle times when handling payloads up to 150kg.
To integrate articulated and linear technology, ABB has removed the first rotational axis from the robotic arm, enabling it to be mounted either upside down or sideways on the linear gantry unit, which acts as the first axis. The ability to be mounted overhead facilitates production flexibility as the linear gantry axis unit can be extended by up to 33m horizontally and 4m vertically. With this extended reach, the robot can access several machine tools without compromising performance, resulting in high productivity and machine utilisation.
Smart or ‘Smirt’?
As always, software has a major influence on facilitating automation in many milling applications. Take press dies for example, which seem to be getting bigger and more complex with each passing year. Here, machining operations certainly aren’t what they used to be, as Ford’s tool and die plant in Dearborn, Michigan can testify.
Since 2004, the plant has seen the hours required to build a die dramatically reduced. As a result, the facility is building more dies in-house than ever before – 20% more dies in 2009 in comparison with 2008. “That’s due to simulation and machining technology,” states Tool and Die Chairman Jeff Laver. Much of the credit for this success, says Terry Henning, Plant Manager, goes to the firm’s widespread acceptance of the package of die-manufacturing planning software from Smirtware Inc, a division of Vero Software. Smirt is purposedesigned for the automotive sector – it is not a generic CADCAM system. It first made its way into the Dearborn facility in 2002; the latest version (V8) was installed in 2009. “Our CPA (construction, planning and analysis) team of die makers develops a procedure for every die we build, then the Smirt DieBuild software provides the instructions for exactly how we want to build each die, step by step,” says Henning. “These instructions route to every subcontracted die shop we use around the world, which also use Smirt (DieShop) as a die design information management tool and 3D viewer. This way we can control how every supplier machines our tools.”
Machinists use Smirt DieNC, an add-on module to DieShop, to create their own programs and derive tool paths for machined faces and drilled holes. “We get better awareness of available machine time, fewer rush jobs and we can more accurately plan for the work, and be proactive,” says Keith Zobay, Superintendent of the Die Construction department.
Machining instructions make their way to the shop floor where operators have access to 20 computer workstations running DieNC. They can view in colour every surface that needs to be machined. The fact that Smirt works with multiple CAD systems provides a common tool to handle all of the die information required for build purposes. The uptake of Smirt in automotive circles is spreading fast. According to Vero Software, it is being used by Ford (US, UK, Germany), Fiat, Honda and Chrysler, among others. At the Shizuoka, Japan plant of Ryobi, manufacturer of die cast products such as gearbox casings and cylinder blocks, the company recently encountered an increasingly common industry problem. Ryobi had been using WorkNC from Sescoi since 2001 for three-axis machining and positional five-axis machining for die production, but due to the depth of the cavities, and the surface quality required, finishing operations necessitated the extensive use of electrodes. Concerns over the difficulty of creating five-axis simultaneous toolpaths and the surface finish that they might produce, had previously prevented a move into simultaneous five-axis machining. However, the high number of hours needed for the production of electrodes led the company to examine ways of machining more of the tool directly, thereby cutting overall production time. The existing manufacturing process consisted of four machining operations, heat treatment, and then further finishing operations, including EDM die sinking, cavity machining and jig boring; a total of 12 operations. To achieve the required savings, Ryobi opted to use WorkNC Auto 5, which reduced 12 operations to just eight.
WorkNC Auto 5 automatically converts three-axis toolpaths to five-axis simultaneous toolpaths, taking into consideration the effective tool length, the geometry of the holder and the rotational limits of the machine tool. For maximum efficiency, Auto 5 leaves three-axis toolpaths unchanged where they can reach the part, optimising speed of machining, tool rigidity and surface finish. With Auto 5, the process of generating five-axis toolpaths is very simple, as the software evaluates the three-axis paths to be converted, performs a collision check and post-processes the resulting toolpath with minimum operator intervention.
Adopting Auto 5 enabled Ryobi to reduce five surface finishing processes to three, while electrode manufacture and EDM die sinking has been much reduced, as the company can now machine the bulk of the cavity. Ryobi also uses Auto 5 starting at the re-roughing stage, using a small tool to pick-out after the initial roughing operations. Due to the reduction in the number of operations, machine downtime is considerably lower, which shortens lead-times, while in total, machining times have been cut by 33%. While no one can predict the future of machining operations, no one sees a future without automation!