Time to be narrow-minded

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With companies under pressure to cut costs and use existing facilities more efficiently, there is a renewed focus on making the most of warehouse space – particularly through the use of narrow aisle or very narrow aisle systems.

Both have a role but there are hard choices to be made in deciding which route to go down.

Mark Ogden, product manager VNA at Toyota Material Handling, points out that “the increase in land and property prices, combined with the scarcity of quality sites in prime locations has driven many companies to consider ways to make the best possible use of the space they already have.

“Racking is getting higher and increasingly our customers are asking us for advice on material handling solutions that reduce aisle space.”

Son Thai, warehouse specialist at Briggs Equipment, says: “There are a number of factors when deciding whether to purchase narrow aisle or VNA trucks. The first is ‘what are the key objectives?’ Consideration needs to be given to what the user is trying to achieve. Does the user want a dedicated machine for the application at hand? And how narrow is the aisle? The size of the aisle can sometimes determine the type of machine used.

“Cost is another important factor when choosing between narrow aisle machines and VNA trucks,” says Son Thai. “The VNA trucks are bespoke machines and are very expensive compared to the narrow aisle trucks. Another consideration is flexibility. With narrow aisle machines or articulated trucks (for instance the Flexi G4) these machines can work in tight aisles as well as having the flexibility of working outside. However, VNA trucks are bespoke machines that are dedicated to a specific application; so once the contract has finished the machine becomes obsolete. As a result, the flexibility of the narrow aisle means that they generally have a higher residual value than the VNA machines, which often have little or no residual value.”

All the suppliers of articulated trucks are reporting increased interest in the concept. Simon Brown, managing director of Translift Bendi, says the number of approaches from companies wanting to explore the possibility of making use of articulated trucks has been rising. And he cites cost savings and more efficient use of existing warehouse space as two big drivers.

Gerry McHugh, managing director of Aisle-Master, highlights the multifunctional nature of the articulated truck – offering both indoor and outdoor operations, working in both conventional and narrow aisles – and opening the way to do the job of two trucks with just one. And he reckons that as trading conditions have got tougher, people have got more time to look at improvements in warehouse operation.

Both Brown and McHugh point to the fact that companies are increasingly looking to reduce off-site or outside storage, and going over to narrow aisle can facilitate this.

McHugh says Aisle-Master has seen a growth in interest from cold stores where, because of the additional cost of maintaining the temperature control, it has become even more important to maximise the use of space. So sales have risen for trucks capable of working at -40ºC.

Steve Richmond, general manager of Jungheinrich’s systems and projects division, points out: “Apart from comparing the storage capacity increases that might be offered by a VNA system against, say, a reach truck-based or wide aisle solution, specifiers should also consider the type of goods that are being handled. Loads are picked and put away in a more controlled manner using a VNA system, so if goods stored are fragile or of high value, then VNA could represent the best option.”

VNA trucks minimise floor area requirement for a given amount of stock and give effective use of the volume of the building. However, Toyota’s Mark Ogden points out that initial purchase cost is high compared to other types of vehicle. “They can be cumbersome to manoeuvre outside the aisle, so many organisations prefer to use counterbalance or reach trucks to feed pick-up and deposit stations at the end of each aisle, restricting the VNA truck to operations within the aisle. This causes some double handling and requires additional vehicles.

“The cost of installing a guidance system within the aisles must also be taken into account. Drive-in racking is a simple solution requiring little additional investment, with a relatively low cost per pallet stored. However, practical utilisation of around 50 per cent and the additional cost caused by damage caused to goods, racking and the trucks themselves mean it is less than ideal for larger operations.

“Mobile racking gives excellent practical utilisation, with 95 per cent of the space being available. We find many companies can be deterred by the high initial investment and ongoing maintenance cost that give a cost per pallet stored that can be almost three times as much as drive-in racking. Operations that require a high throughput can also find that their space utilisation ends up much lower than 95 per cent,” says Ogden.

With a high cost per pallet stored, flow racking is more suited to facilities that can operate on a purely first in first out basis, but offers the real benefit of high throughput. Once again up front investment and ongoing maintenance costs can rule this option out for some.

Richmond points out that when designing a storage solution, many operators are driven by the need to maximise pallet capacity within the store. “However, there are other aspects that should always be considered, such as the product profile and the range of SKUs that are held. Generally speaking, operations where low order volumes are being picked – such as e-fulfilment sites – do not suit VNA systems.

“We always advise our customers to consider any peaks they have in their business and how they’ll manage them. In may cases, a warehouse will operate at in the region of 70 per cent of its capacity for most of the year and then at the busiest times this might leap to 120 per cent.” lot of cases, high lift articulated forklift trucks have replaced VNA man-up machines. Articulated trucks can now be supplied with strong fixed mast tilting carriages and this – combined with the huge advances in operator vision system technology that enable a crystal clear picture of the highest pallets to be transmitted to the operator’s in-cab screen – enables pallets to be picked and put-away up to 12 metres high while permitting first and second level order picking to be carried out safely and efficiently within the same aisle.

“Developments in powered mobile racking have also helped to make the case for the articulated forklift a compelling one. For example, Narrow Aisle has recently provided articulated trucks to a third party cold store operator where the combination of powered mobile racking and Flexi trucks has allowed 6,200 pallet locations to be provided. Tests showed that use of static narrow aisle pallet racks and traditional VNA machines at the same site would have restricted the facility’s capacity to 5,000 pallets.”

Mark Ogden highlights a number of factors that need to be taken into account including:

• Man-up or man-down: Man-up trucks such as the BT Vector range, keep the operator close to the load and allow order picking to be carried out at all levels. However, they generally represent a larger investment than a man-down truck such as the BT Veflex.

• In-aisle guidance: VNA trucks require some form of guidance in the aisle. This normally takes the form of steel rails bolted to the floor, or a wire embedded in the floor which emits radio signals which are used to guide the steering actuators of the truck.

• Fork options: The BT Veflex man-down truck from Toyota has the option of either rotating forks, which turn to access the aisles either side of the truck or shuttle forks, which can travel backwards and forwards to position pallets. While shuttle forks can operate in even narrower aisles than rotating forks, they require top brackets to be fitted to the racking beam to allow the forks to access the pallet.

Jungheinrich’s Steve Richmond emphasises the importance of the whole life cost of a VNA machine. “A VNA truck may be initially more expensive than alternative options but the user must consider a host of other often less than obvious cost savings that VNA trucks will bring, such as reduced product and equipment damage and the fact that it takes less time to train an operator to use a VNA machine.

“There may also be significant cost savings to be made in the overall design and build cost of a new facility by using a VNA system. For example, a reach truck might be able to serve racking up to 12 metres high but a VNA system can go to 16 metres.”

However, John Maguire reckons that to be efficient, “man-up Combis require long, uninterrupted aisles that allow the units to lift and lower while travelling between pallet positions and, although they are designed to allow single-item picking, as well as handle entire pallets, Combis arguably work best within high bay stores putting away and retrieving full pallet loads.

“Furthermore, low level order picking in the same aisle at the same time as a man-up truck is working can be dangerous because the man-up machine’s elevated operator position makes it difficult to see an order picker working at ground level – with all too obvious potential consequences. Many of the difficulties created by low level order picking within a guided VNA system can be overcome by the use of articulated trucks. “While they require slightly wider aisles than VNA man-up Combis, articulated trucks offer distinct advantages at sites where there is a need to low level order pick at ground-level stock locations. For example, the actual aisleway is not constrained by guidance systems and fixed stacking depths/traverse strokes so the whole building width can be used. By incorporating bridged intersections into the racking design, say, every 30 metres, low level order picking and pick face replenishment is dramatically improved and congestion in the aisleways minimised.”

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