In automotive assembly plants, there is sometimes a misconception that the paint operation is the most critical since it is the final process everyone sees. This is only partially accurate. Body-in-white is the first step, and it sets the foundation for e-coat, primer, basecoat, and clearcoat. If manufacturers don’t identify and remove defects in body-in-white, the paint processes can accentuate imperfections or create paint defects. Repair costs are compounded when defects are not identified and removed only in the painting processes.
Body-in-white consists of two critical machining processes: rough grind and metal finishing. Rough grinding can include blending mismatch and removing or leveling metal flash, tabs, and excessive tack weld. Metal finishing produces the final finish for the rough grind areas and removes and finishes minor defects such as in-dings (above or below the surface) due to stamping or handling. In-ding areas are typically found on hoods, roofs, doors, fenders, quarter panels, and trunk lids – critical aesthetic components that are in the driver’s line of sight.
Under and over-processing
Achieving Class A surfaces in automotive applications is a typical Goldilocks situation – too much or too little repair leads to problems, so companies have to get the results just right.
If the defect is under-processed, file marks or circular scratches not completely removed will telegraph through the paint layers. This is a common defect identified in the e-coat process, and they can be removed at a relatively low cost.
Over-processing defects can lead to a mar – a smooth and shiny area on the surface. The mar must be manually scuffed with a fine grit abrasive in an e-coat or primer application. Otherwise, the basecoat (paint color) will not cover the sanded area identically to the non-sanded area, resulting in off-color flaws. Since basecoat and clearcoat are the final two paint processes, off-color flaws can become major defects that don’t get identified until final inspection. This requires the vehicles to be taken off-line to be repaired – a costly process due to the labor, materials, and time.
The start to most body-in-white repairs, rough grinding is typically completed with a right-angle sander at 6,000rpm using a resin fiber disc (F980) or a D-weight paper disc (A995), depending on the severity of roughness. Next it is blended with a random orbital sander, also known as a DA Sander, at 12,000rpm with a 3/16" orbit using a B-weight paper disc (A275/A975).
When the rough defect process is completed, the area is finished with a random orbital sander (DA) with a 3/16" orbit to remove file marks or circular scratches. The random orbital sander should be started on the vehicle to avoid gouging. It should be used with an uninterrupted motion, applying medium-to-intermediate pressure to remove file marks or circular scratches, and feather outward. Defects should never be removed at an angle to the surface, because it will cause severe gouging or deep, wild scratches.
As with any grinding, blending, or finishing operation, all aspects of the process are imperative to the right finish. The right-angle sander, type of file, random orbital sander, air supply, air hose, back-up pad, and the abrasive itself all play an integrated role. Any one of these on its own and improperly selected can cause a defect to the workpiece. Right-angle sanding or random orbital finishing processes are critical, manual operations where operators must rely on their ability to remove surface defects and produce consistent finishes at high production line rates.
The foundation of the paint process in a prime automotive plant commences in the body-in-white shop. If the defect removal process is not properly executed – to account for under- or over-processing – the end result will be a paint defect.
High-torque electric motors put added strain on powertrain components such as shafts and splines. The additional forces, combined with the need for higher rotational speeds and greater concentricity to reduce noise, vibration, and harshness (NVH), have made specs for electric vehicle (EV) and hybrid powertrain suppliers extremely challenging. Lightweight requirements for all components heighten the challenge as automakers request hollow designs for many rotating parts.
DVS Production in Krauthausen, Germany, maker of 20 million transmission parts per year for the international automotive industry, meets those demands with hard-fine machining of complex hollow shafts. Using flexible, multi-function turrets on its machines, the company produces parts with dozens of machined features: OD grinding, hard turning, surface facing, milling, and seal-seat grinding (see Fig. 1, below).
The supplier, a member of Germany’s DVS Technology Group, relies on DVS UGrind series machines from group partner Buderus Schleif- technik in Asslar, Germany. Developed for the hard-fine machining of small- to medium-sized series of shafts and lining parts, the machine series combines grinding, turning, milling, and measuring in one clamping.
Complex manufacturing challenge
Cubic boron nitride (CBN) high-performance cutting materials are reducing grinding process times by permitting faster cutting speeds while increasing grinding tool service life. When manufacturing small- to medium-sized batches, which are usual for the series production of powertrain components for electric vehicles, optimizing processes relies less on tool service lives and more on reducing non-machining times, such as changeovers between the first workpiece clamping and the final finishing processes.
A multi-functional turret on DVS’ UGrind machines can reduce machining time for multi-featured components up to 50%. Compact components minimize non-cut travel times for grinding, turning, milling, and measuring. An integrated measuring probe controls machining to achieve the required final dimensions, eliminating successive feeding and re-measuring steps.
Hollow, heavily machined shafts
More stringent shape and position tolerances for EV components require maximum manufacturing precision. First, a measuring probe on the UGrind’s turret with a 270° radius of action establishes a level surface to determine the exact axial and rotation position of the workpiece. The control system then calculates optimum feeding and forwarding parameters, after which the key surface is manufactured using a CBN hard milling tool. Then, a combined turning steel holder with two blades performs high-precision hard turning of various flat surfaces on the left and right, followed by CBN grinding of several ODs to micron tolerances. For precise grinding of the long outer diameter, plunging takes place at several points, followed by peel grinding from left to right.
An extremely fine grit CBN grinding disc finishes the hollow shaft’s seal seat, achieving a surface roughness of Rz<1µm. In-process measuring equipment measures a reference OD, and other ODs are traced following this reference. Executing all machining operations in a single clamping reduces setup times and the number of manual handling steps, avoiding re-clamping faults. Using high-quality, high-performance tools and short travel paths can minimize cycle times.
A 6-axis robot with 1.6m range manages the machine. The robot loads and unloads pre-positioned hollow shafts from a conveyor system. A camera system permits precise part detection using a dot matrix code – offering the customer exact traceability of each hollow shaft. For worker safety, a sensor-controlled system shields the working chamber using optical barriers, guaranteeing the loading and unloading process comes to a standstill if an object enters the protected area.
More than a year after promising to revisit Obama-era fuel economy rules, President Donald Trump’s administration has taken steps to restart the rulemaking process. Obama-era rules set in 2012 mandated 54.5mpg average fuel economy by 2025, a standard that many automakers have complained is unworkable.
With several offset credits, for activities such as updating refrigerants for air conditioning systems, real-world requirements were closer to 45mpg. However, without many buyers opting for electric vehicles, even that lower number was a major challenge (see Rearview, pg. 58).
Automakers agreed to the higher standards in 2012, in part, because regulators included a midterm evaluation (MTE) process that would give them the chance to lobby for more realistic standards in 2017 and 2018. However, in the final days of his administration, Obama’s EPA sped up the MTE process, saying the 54.5mpg figure should stand.
U.S. Environmental Protection Agency (EPA) Administrator Scott Pruitt has ruled that Obama’s MTE was faulty, effectively throwing out that determination. While automakers and car dealers praised the decision, environmental groups attacked it.
“Obama’s EPA cut the MTE process short with politically charged expediency, made assumptions about the standards that didn’t comport with reality, and set the standards too high,” Pruitt said.
In addition, Pruitt threatened to cancel a waiver to federal emission rules that allows the California Air Resources Board (CARB) to set higher emissions standards than the federal government. Twelve other states follow California’s lead, effectively creating two standards. Automakers agreed to the higher 2012 standards, in part, because of the promise to harmonize CARB with the EPA.
“Cooperative federalism doesn’t mean that one state can dictate standards for the rest of the country. EPA will set a national standard for greenhouse gas emissions,” Pruitt said.
Lawmakers in California and states that follow its standard have threatened to sue if the EPA revokes the waiver that allows those states to set higher emissions and fuel economy standards. CARB Chair Mary D. Nichols called Pruitt’s actions “a politically motivated effort to weaken clean vehicle standards with no documentation, evidence, or law to back up that decision.”
The EPA’s decision had been expected for more than a year, following Trump’s announcement that the agency would reconsider the Obama ruling. In filings rejecting the late 2016 findings from the Obama administration, Pruitt relied heavily on comments from automakers and lobbying groups, mostly the Alliance of Automobile Manufacturers. Those groups have argued that many of the EPA’s 2012 market assumptions have proven to be wrong.
Fuel economy has improved in the past six years as automakers have slashed vehicle weights; increased the use of smaller, turbocharged engines; and increased the use of 8-, 9-, and 10-speed automatic transmissions. However, sales of hybrid and electric cars have not become a significant source of sales, and consumer tastes have shifted from cars toward trucks, sport utility vehicles (SUVs), and crossovers.
The ruling effectively restarts the process, giving automakers and industry groups a chance to argue for changes to future efficiency mandates. Pruitt did not provide a timeline for how quickly the EPA will develop new rules. www.arb.ca.gov; www.autoalliance.org; www.epa.gov
Electric drive ownership stagnates in California
Departments - Rearview
Despite incentives, higher availability of vehicles, most green vehicles are sold to those who already own one.
In 2017, several automakers and policymakers announced commitments to transition to electric vehicles (EVs) – Toyota, 1 million EVs by 2030; Volvo, 1 million EVs by 2025; Volkswagen, 25% of vehicle sales to be EVs by 2025. Norway has called for all new cars to be electric by 2025; France, the United Kingdom, and California aim to achieve the same by 2040.
Meanwhile actual sales are tiny. A total of 780,000 on-road plug-in electric vehicles (PEVs) have been sold in the U.S., representing 0.3% of the nation’s 243 million passenger cars and light-duty trucks. In California, less than 1% are PEVs. PEVs accounted for only 1.1% of U.S. vehicle sales in 2017 and were on track to be less than 5% of sales in California. Many of these are repeat sales to the same households, so an even smaller percent of households are adopting these vehicles.
There are no paths to meet the PEV commitments unless consumers are engaged in the transition to electric drive. Evidence from California says consumers are not. The number of car-owning households that are paying attention to PEVs is not growing.
In five surveys conducted from June 2014 to June 2017, the Plug-in Hybrid & Electric Vehicle Research Center of the UC Davis Institute of Transportation Studies assessed Californian attitudes on electric drive. In 2014, 5% already owned a battery-electric vehicle (BEV) or had actively shopped for one. About another 13% said they had gathered some information about BEVs but were not seriously considering one. Those figures are not higher to any significant degree for 2017.
What about the increasing number of makes and models of PEVs offered for sale between 2014 and 2017? According to the California Air Resources Board’s Drive Clean website, this nearly doubled between 2014 and 2017. However, in 2017, fewer Californians were able to name a PEV for sale compared to 2014. Awareness of incentives? Not higher in 2017 than in 2014. Percentage of car-owners who understand how hybrid, PHEV, and BEVs vehicles are fuelled? Not higher.
Californians are not deciding against PEVs, but they remain unaware of PEVs and anything about them. Millions of California households are simply not engaged in any transition to PEVs.
Pillow blocks and flange blocks feature a lubrication fitting and an alignment set screw. Stainless steel and self-aligning linear bearings are modified with an alignment flat ground on the bearings’ outer shell and drill a hole through the outer shell. Lubricants are pumped directly inside linear ball bearing races without removing the bearing from the shaft. Pillow and flange blocks also accommodate an encapsulated ETX scraper seal, preventing contaminants from getting inside the bearing and retains the lubricant in the bearing.
Pillow blocks are available in closed single- and double-bearing models for 0.5" to 2.0" shafts. Flange blocks are available in single and double bearing models for 0.5" to 1.25" shafts. Other options include untreated aluminum or corrosion-resistant nickel coating.
WavyJoint cubic boron nitride (CBN) inserts offer higher productivity in hard turning operations, enabling a single pass at a large depth of cut and high feed rate. They achieve depth of cut up to 0.8mm with fewer turning passes, resulting in higher efficiency.
A work-in-process (WIP) cart holds small batches of large and small sheet-metal parts as they go through various stages before final assembly.
Three of the compartments are tall for the largest components, while the other nine are shorter to hold different part sizes. The plastic floor and panels provide part separation and minimize part movement.
The cart features four 4" swivel casters with urethane wheels. Two of the casters have brakes for secured positioning.
Higher capacity and custom cart sizes are available, along with various colors for visual identification by department, product line, shift, and associate. They can also be configured for electrostatic discharge (ESD) (anti-static) applications.