Physical test procedures for forklift trucks by KION brand companies

A single circular track. The air is filled with continuous engine noise, interspersed with the rumbling of solid rubber tires on hard ground. The test center in Aschaffenburg, operated by Linde Material Handling, a subsidiary of intralogistics company KION, presents a striking picture. Attached to a pivot point at the center of the track by a steel cable, a driverless, unsuspended forklift truck has been going around in circles for days. It is something of a baptism of fire: This truck is in the development process and is being tested under extreme conditions. Ridges have been added to the circuit to simulate bumpy ground, which puts the truck and all of its components under significant stress. Portions of this test are conducted with maximum load, others with no weight on the fork at all, in order to reflect different load conditions.

KION subsidiary STILL conducts similar tests at its test center in Hamburg. On a circular track with a diameter of sixteen meters, each tested truck completes thousands of laps. In addition, the Hamburg test center has ‘poor surface tracks’ that are used to test suspended chassis designs for tug trucks. At its two traditional forklift truck plants in Germany, the KION Group has extensive infrastructure in place to put trucks through their paces.

Vehicle tests are a familiar concept and have been widely reported on in connection with car manufacturing. Most people have probably seen some slow-motion footage of crash test dummies slamming into airbags. The scenes that unfold at the KION test centers are every bit as spectacular – imagine heavy piles of timber crashing down onto vehicle roofs and trucks driving around with counterweights covered in thick blocks of ice. These tests serve a variety of purposes. They help to guarantee the functionality of the forklift trucks, make them as safe as possible, and ensure that they can endure a long life of 20,000 hours of operation.

For more than 35 years, KION’s forklift truck brands have been conducting extensive testing both at the development stage and during series production. The tests cover everything from safety systems and assistance systems to drive technology, chassis, and hydraulics. Individual components and fully assembled trucks have to endure many thousands of hours of testing under the watchful eyes of the experts in Aschaffenburg and Hamburg in order to prove that they meet all requirements and fully comply with CE standards. Do all truck components function the way they should? Does the truck meet all ergonomic requirements? And how well does the truck cope with risk scenarios that may occur in a warehouse?

The latter is examined, for example, as part of standard safety tests by Linde MH and STILL. The trucks are positioned on platforms specifically designed for this type of test. A steel platform, for example, can be tilted to simulate one of the most critical situations in everyday intralogistics operations: a fully extended lift mast, heavy loads, and uneven ground – a potentially disastrous combination. All kinds of scenarios are simulated with the help of these platforms, from low loads on a steeply tilted surface and high loads on a lightly tilted surface to extreme scenarios where very heavy loads are raised up very high on the fork and erratic driving movements could throw the forklift truck off balance. The test design allows for all of these risks to be simulated in a safe environment. Insights gained from these tests are then taken into account in the development process in order to improve the stability of trucks in a targeted manner.

Another, equally dangerous scenario that can arise as part of normal warehouse operations is goods on the upper shelves of a high-bay storage facility becoming dislodged and falling down onto the forklift truck. This scenario is simulated by means of an ‘impact drop test’ that tests the resilience of the overhead guard. Heavy bundles of timber are purposefully dropped onto the forklift truck. After the impact, the permanent deformation of the material is measured. To pass the test, the damage needs to remain below a defined standard value.

It is not just the vehicle as a whole that undergoes targeted testing to assess functionality, safety, and durability, but also individual components. Lift masts, for example, are put through a very tough testing regime by experts in Aschaffenburg and Hamburg. In component test rigs specifically designed for this purpose, they continually perform typical operating maneuvers for twelve to 15 weeks. In order to obtain approval, the lift masts need to complete several tens of thousands of test cycles, i.e. more than 100,000 lifting actions, all at maximum lift speed and load. The drive axles have to endure a similar treatment. A hydropulse test system is used to put strain on the component in critical places in a way that simulates intense daily operation, albeit at a greatly accelerated pace.

Electrical components also undergo testing, for example the converters that transmit electricity from the battery to the drive system components and regulate the power in forklift trucks. In a dedicated appliance at the Hamburg test center, this core component of any electric drive system is operated continually for 24 hours a day for 365 days on end – a full year of non-stop strain. The converters are thus subjected to ‘permanent stress’ at maximum performance in order to ensure that the components used in the trucks are sufficiently robust to withstand any stress that may arise during operation by the customer.

The lithium-ion batteries used in the vehicles manufactured by KION’s forklift truck brand companies are subjected to testing too. Some of these tests are required by law and focus on the safety and performance of the batteries. In Hamburg and Aschaffenburg, batteries undergo purpose-designed test cycles that simulate specific stress levels. Battery performance is measured throughout this process. However, the KION Group frequently goes far beyond the statutory minimum requirements. A test conducted in open terrain in Aschaffenburg is an (extreme) case in point. A small, compact electric forklift truck fitted with a lithium-ion battery is placed in the testing area. Then, an extra heavy-duty truck with a total weight of about 24 tonnes is accelerated to maximum speed and sent crashing into its ‘little brother’ without braking. Accompanied by a lot of clanking and crunching, the tips of the fork arms hit the body of the smaller truck exactly in the area where the battery compartment is located. Nonetheless, there are no sparks to be seen and the housing of the battery compartment easily withstands the brutal impact. This is definitely not an everyday warehouse scenario, but the KION Group ensures that its tests cover even the most extreme events.

Requirements vary depending on the environment and the forklift trucks manufactured by the KION Group are used all over the world. At fishing ports in Norway, STILL forklift trucks are being used in freezing temperatures. In other regions and production environments, for example in foundries, trucks are exposed to intense heat. The test centers in Aschaffenburg and Hamburg can also simulate these extreme conditions. Very high temperatures can put a huge strain on forklift trucks, so it must be ensured that the cooling system works properly. The experts have therefore devised tests that take the trucks and their drivers to their limits. On a purpose-designed track, the industrial truck is being driven back and forth between two bays, carrying a high load. The process also involves the load being lifted and lowered and all steps are carried out at maximum performance. The conditions of this test are so tough on the truck driver that several people take turns in the driving seat to complete each test cycle. All of this serves to ensure that the temperature measured on the truck does not exceed a critical threshold and that the truck does not overheat, even if ambient temperatures are as high as 45°C – extreme conditions for the machines and the people who operate them.

Sub-zero temperatures also present challenges. Does the engine of an internal combustion truck start reliably in very cold conditions? Can electric forklift trucks deliver full performance at temperatures below freezing? Is the lift mast always fully operable? One of the main issues that needs to be resolved for functionality in cold environments is the viscosity of the hydraulic oil. The viscous oil needs to be moved and circulated by the pumps in order to prevent a complete standstill. In Aschaffenburg and Hamburg, experts have recreated these exceptional conditions in the test center. The forklift truck is left in a cold chamber at minus 20°C for twelve hours. The requirement is for the internal combustion engine to start without a hitch at the end of this ordeal.

Unfortunately, not all field conditions can be recreated reliably in a test center. Sometimes, it takes a journey of several hundred kilometers to find the right conditions. On the slopes of the Grossglockner mountain, at an altitude of 2,500 meters, the KION Group is the only mechanical engineering company to join many well-established names from the automotive industry in a common endeavor. They all seek to test vehicles with internal combustion engines at high altitude, where the air is thin and temperatures are low. This is the ultimate stress test for diesel-powered industrial trucks and it highlights the importance of ensuring that vehicles can remain operable even under extreme conditions. Thin air reduces the performance capacity of internal combustion engines. The engine must be able to start reliably from cold and compliance with emissions standards must be ensured. When temperatures on the slopes of the Grossglockner drop below freezing, the forklift trucks are being taken to their limits – and the trucks manufactured by Linde and STILL pass these tests with flying colors.

Alongside the various procedures used to test materials, digital simulations are also becoming increasingly important. Part two of this report explores where the KION Group stands on the subject of virtual testing.